Glossary
Every domain and tool term the course uses, defined in plain language. Lessons link here the first time a term appears.
Purpose: Every domain and tool term used in the course is defined here, plainly, with a one-line definition and a short example. Lessons link into this file via the vocab callout pattern: **term** (definition, [→ GLOSSARY](GLOSSARY.md#term)). Each anchor below corresponds to a vocab callout used in a lesson.
Structure: Alphabetized within each section. Each entry has the format:
term
One-line plain-English definition. Example or context. Used in:
[→ source lesson](path/to/lesson.md).
How to contribute: See CONTRIBUTING.md. The norm is: when a lesson uses a term for the first time, the lesson author adds an entry here in the same PR. If you find a vocab callout in a lesson without a matching anchor here, file an issue or PR a fix.
A
agent-loop
The iterative cycle of intent → ask → evaluate → steer, repeated until the AI agent has produced what you wanted. Example: every Module 3 lesson is one or more iterations of the agent loop. Used in: Module 3 — Introducing the loop.
ai-coding-agent
A program that reads your project files, plans changes, and writes code on your behalf — guided by a conversation with you. Example: Claude Code and Gemini CLI are the two AI coding agents this course uses. Used in: Module 0 — Welcome.
api
The contract between two programs about which questions can be asked and how the answers will look. Example: "the Twitter API supports GET /2/tweets/:id."
Used in: Module 1 — Where data lives, how programs talk.
api-key
A long string that identifies your account when a program calls a paid (or rate-limited) service on your behalf. Treat it like a password: never paste it into chat, never commit it to a public repo. Example: a Gemini API key starts with AI...; an Anthropic API key starts with sk-ant-....
Used in: Module 0 — Account creation.
app-router
The newer routing system in Next.js, where files in the app/ folder define URL routes. The older system used a pages/ folder; both still work, but App Router is the modern default. Example: app/page.tsx is the home page; app/about/page.tsx is the /about page.
Used in: Module 3.5 — Reading a file tree.
ask
The "ask" step of the agent loop — writing a specific request the agent can act on, given the intent. Example: turning the intent "I want today's date below the tagline" into the ask "Add today's date below the tagline in modules/03-the-loop/scratch/index.html."
Used in: Module 3 — Introducing the loop.
authentication
Confirming you are who you claim to be. Sometimes shortened to "authn." Example: a password check, or clicking a magic link sent to your email. Used in: Module 1 — Who can do what.
authorization
Deciding what an identified user is allowed to do. Sometimes shortened to "authz." Example: a logged-in user can edit their own posts but not someone else's. Used in: Module 1 — Who can do what.
B
branch
An independent line of commits in a git repository, used to try a change without affecting the main history. Example: git checkout -b add-login creates and switches to a new branch named add-login; commits on that branch do not show up on main until you merge.
Used in: Module 2 — git and GitHub.
browser
A program on your computer that knows how to ask servers for webpages and render them. Example: Chrome, Firefox, Safari. Used in: Module 1 — How the web works.
C
ci-cd
Continuous integration / continuous deployment. The automated path from "I committed code" to "it's live on the internet." Example: pushing to main triggers Vercel to build and deploy your Next.js app.
Used in: Module 1 — How it goes live.
claude-code
Anthropic's command-line AI coding agent; this course's recommended primary agent. Example: install on macOS or Linux with curl -fsSL https://claude.ai/install.sh | bash; on Windows in PowerShell with irm https://claude.ai/install.ps1 | iex.
Used in: Module 2 — AI coding agents.
client-component
A Next.js file that runs in the browser and supports interactivity — useState, onClick, forms, anything that responds to user input. Marked by 'use client' on the first line. Example: app/components/InteractiveButton.tsx in Module 3.5's sample-app uses useState and an onClick handler, so it's a Client Component.
Used in: Module 3.5 — 'use client' and the server/client split.
code-editor
A program that lets you read and edit source files with niceties like syntax highlighting, search across files, and integrated tools. Example: Visual Studio Code (VS Code) is the editor a Codespace presents in your browser. Used in: Module 0 — Hardware check.
codespace
A development environment GitHub runs for you on a remote machine; you reach it from your browser, but the files and commands live on a computer GitHub manages. Example: opening this course's repo and clicking Create codespace on main boots a Codespace with the editor and terminal ready.
Used in: Module 0 — Hardware check.
commit
A saved snapshot of changes in a git repository, with a one-line description. Example: git commit -m "add login button" creates a commit containing every file you previously staged with git add.
Used in: Module 2 — git and GitHub.
context-window
The amount of text an AI agent can see at once — your conversation history plus any file content it has loaded. Finite; as the conversation grows, older parts scroll out. Example: Claude Code shows current usage via /context; Gemini CLI shows it via /stats.
Used in: Module 3 — Planning vs execution conversations.
cookie
A small piece of data the browser stores and re-sends to the same site on every request. Example: a session cookie tells the server "this is the same Alice who logged in 5 minutes ago." Used in: Module 1 — Who can do what.
D
database
A program that stores structured data in tables and answers queries about it. Example: PostgreSQL, Supabase's database engine. Used in: Module 1 — Where data lives, how programs talk.
dependency
A package your project NEEDS to run, listed under dependencies in package.json. Example: the Module 3.5 sample-app's package.json lists next, react, and react-dom as dependencies.
Used in: Module 2 — The package manager (npm).
deployment
The act of moving an app from a developer's laptop (localhost) to a public server so anyone on the internet can reach it. Example: pushing to GitHub and letting Vercel build and host the result. Used in: Module 1 — How it goes live.
diff-summary
A one-line per-file report from an AI coding agent showing the filename and the number of lines added or removed. Example: Modified: app/components/Footer.tsx (+1 line, -1 line) — the filename plus the counts; you do not have to open the file to spot a wrong-file edit.
Used in: Module 3.5 — Spotting wrong-file edits.
directive
A special single line at the top of a file that changes how the file is treated by its framework. Example: 'use client' is a directive that tells Next.js a file is a Client Component.
Used in: Module 3.5 — 'use client' and the server/client split.
dns
Domain Name System — the system that translates a human-readable URL into the IP address of the actual server. Example: when you type example.com, DNS resolves it to 93.184.216.34 so the browser knows which server to ask.
Used in: Module 1 — How the web works.
drift
When an AI agent loses the thread of what it agreed to do — usually after a long session, after several scope-changes, or after the conversation history fills up. The agent stays fluent and confident, but starts working against an outdated version of the plan. Example: an hour into a session, the agent edits a file you told it to leave alone, because the "leave it alone" instruction is no longer in its working memory. Smell-test surface: Module 3 Lesson 2. Recovery move: /clear and a tighter restart, taught in Module 3 Lesson 4.
Used in: Module 2 — AI coding agents.
E
error-message-anatomy
The structure of a typical error message: a description on top followed by a stack trace listing file paths and line numbers. Example: a TypeError: Cannot read properties of undefined with stack frames pointing at app/components/InteractiveButton.tsx:5:18.
Used in: Module 3.5 — Error message to file pointer.
evaluate
The "evaluate" step of the agent loop — reading the agent's output and deciding if it matches your intent. Example: the agent says it added today's date; you check the page and confirm the date is there. Used in: Module 3 — Introducing the loop.
execution-conversation
An AI-agent session where you ask the agent to actually make the change. Distinct from a planning conversation (no code-writing) which often precedes it. Example: "OK, please proceed with the plan" opens an execution conversation. Used in: Module 3 — Planning vs execution conversations.
F
file-panel
The editor's source-control or file-tree panel showing which files have just changed, often with an M marker or color highlight. Example: when an AI coding agent edits app/components/Footer.tsx inside a Codespace, VS Code's source-control panel shows that file with an M marker so you can spot the change at a glance.
Used in: Module 3.5 — Spotting wrong-file edits.
file-tree
The hierarchical structure of files and folders in a project, displayed as an indented list in an editor's left panel. Example: a Next.js project's file tree shows app/, app/components/, package.json, and tsconfig.json at a glance.
Used in: Module 3.5 — Reading a file tree.
foreign-key
A field in one row that points at the id of a row in another table. Example: a posts row's author_id points at a row in the users table.
Used in: Module 1 — Where data lives, how programs talk.
free-tier
The portion of a paid service you can use at no cost — usually capped by hours, requests, or rate limits. Example: GitHub Codespaces' free tier covers 120 core-hours per month before billing kicks in. Used in: Module 0 — Cost-path triage.
G
gemini-cli
Google's open-source command-line AI coding agent; this course's genuinely-free path (Path 2 in BUDGET.md). Example: install via npm install -g @google/gemini-cli on any platform with Node 20 or newer.
Used in: Module 2 — AI coding agents.
git
A tool that tracks every version of every file in a project. Used to commit changes locally and push them to GitHub. Example: git commit -m "add login button".
Used in: Module 1 — How it goes live.
github
A website that hosts code repositories and runs developer tools (like Codespaces) on top of them; Vercel and other deploy services watch GitHub for new code. Example: this course lives in a GitHub repository at github.com. Used in: Module 0 — Welcome, Module 1 — How it goes live.
H
hallucination
When an AI agent produces specific details that look correct but were invented — book titles, function names, API endpoints, file paths the agent has no way of knowing. Example: in Module 3 Lesson 3, both agents invented "favorite books" for a list, even though neither agent has any way of knowing the learner's actual favorites. Used in: Module 3 — Reading plans + recognizing wrong output.
html
The markup language that describes the structure of a webpage — a tree of elements like headings, paragraphs, links, and images. Example: <h1>Hello</h1> is an HTML element.
Used in: Module 1 — How the web works.
http
The protocol the web uses to send requests and responses between a browser and a server. Example: clicking a link sends an HTTP GET request.
Used in: Module 1 — Where data lives, how programs talk, Module 1 — How the web works.
http-method
The verb on an HTTP request — GET, POST, PUT, DELETE — that says what kind of operation you're asking for. Example: GET /posts says "show me the posts"; POST /posts says "here's a new post; please save it."
Used in: Module 1 — How the web works.
http-status-code
A three-digit number summarizing how an HTTP request went. Example: 200 OK means success; 404 Not Found means the resource doesn't exist; 500 Internal Server Error means the server crashed.
Used in: Module 1 — How the web works.
hydration
SYMPTOM-only at the M3.5 floor: a message in the browser console meaning "the page does not agree." Treat as a synonym for "a touchscreen file (one with interactivity) is missing the 'use client' label on line 1." The deeper mechanic — how the framework reconciles server-rendered and client-rendered output — is the agent's job and Module 7's curiosity track. Example: a "Hydration failed" error in the browser console is usually a touchscreen file missing 'use client'.
Used in: Module 3.5 — 'use client' and the server/client split.
I
ide
An editor that bundles a text editor, a file browser, a terminal, and language-aware tooling into one program. The "I" is for "integrated." Example: Visual Studio Code (VS Code), the editor inside your Codespace, is the IDE this course uses. Used in: Module 2 — The IDE.
intent
The "intent" step of the agent loop — knowing what you are trying to build before you start asking. Example: "I want today's date below the tagline" is intent; "make the page nicer" is not. Used in: Module 3 — Introducing the loop.
J
jsx
The HTML-like syntax inside React component files. JSX lets you write <Button /> directly in code; the React runtime turns it into the actual button element in the browser. Files containing JSX usually end in .tsx (TypeScript + JSX) or .jsx (plain JavaScript + JSX). Example: <h1>Hello</h1> inside a .tsx file is JSX.
Used in: Module 3.5 — Reading a file tree.
L
localhost
A URL that means "this same computer." Not visible from the public internet — only the laptop running the dev server can reach it. Example: localhost:3000 while running npm run dev.
Used in: Module 1 — How it goes live.
M
markdown
A way of writing formatted documents using simple punctuation marks like # for headings, * for emphasis, and triple-backticks for code blocks. Example: this course is written in markdown; you can read the source on github.com.
Used in: Module 0 — Hardware check.
merge
The act of combining the commits from one git branch into another. Example: git merge add-login brings the commits from the add-login branch into whichever branch you are currently on.
Used in: Module 2 — git and GitHub.
N
next-js
A popular framework for building web apps. Bundles React, routing, and server-rendering into one tool. The framework the thread project in Phase 3 uses. Example: the read-only scaffold at modules/03.5-reading-code/sample-app/ is a tiny Next.js project shown for reading practice.
Used in: Module 3.5 — Reading a file tree.
node
The standard runtime for JavaScript code outside the browser. Example: node --version in a Codespace prints the installed Node version; this course pins Node 20.x LTS in VERSIONS.md.
Used in: Module 2 — The runtime (Node).
npm
The standard package manager for JavaScript code; bundled with Node. Example: npm install downloads everything listed in package.json into a node_modules/ folder.
Used in: Module 2 — The package manager (npm).
O
over-engineering
When an AI agent does MORE than asked — suggesting frameworks, libraries, image lookups, or fancy designs for a small request. The fix is a scope-tightening steer that names the limit ("no frameworks", "inline CSS only", "nothing else"). Example: in Module 3 Lesson 4, the open-ended ask "make the list look like a real bookshelf" prompted both agents to suggest CSS frameworks and image lookups — over-engineering compared to the simple inline-CSS solution the learner wanted. Used in: Module 3 — Steering and recovery.
P
package
A bundled bit of reusable code, published to a registry so any project can pull it in. Example: date-fns is a package that handles date formatting; next is a package that provides the Next.js framework.
Used in: Module 2 — The package manager (npm).
package-manager
A tool that downloads and tracks the code your project depends on. Example: npm is the package manager this course uses; pnpm is an alternative the deferred course platform uses. Used in: Module 2 — The package manager (npm).
planning-conversation
An AI-agent session where you ask the agent to describe what it WOULD do without writing code yet. Example: a prompt starting with "Plan:" and ending with "don't write code yet" opens a planning conversation. Used in: Module 3 — Planning vs execution conversations.
prompt
The specific text you send to an AI agent describing what you want. Example: "Add today's date below the tagline" is a prompt; a series of prompts plus the agent's responses is a session. Used in: Module 3 — Introducing the loop.
pull
Fetch commits from a remote git host (like GitHub) and merge them into your local copy. Example: git pull at the start of a coding session brings down any commits you (or someone else) pushed from another machine.
Used in: Module 2 — git and GitHub.
push
Send commits from your computer to a remote git host. Example: git push after a commit makes the snapshot visible on GitHub to anyone with access to the repository.
Used in: Module 2 — git and GitHub.
Q
query
A written question asking the database for specific rows. Example: a SQL query like SELECT * FROM posts WHERE author_id = 7.
Used in: Module 1 — Where data lives, how programs talk.
R
rate-limit
A cap on how many calls you can make to a service in a window of time, after which the service refuses or delays your calls until the window resets. Example: the Gemini CLI free tier enforces daily caps on requests-per-minute and requests-per-day. Used in: Module 0 — Cost-path triage.
react
The JavaScript UI library Next.js is built on. React components are reusable pieces of UI (buttons, headers, sections) written as files. Example: app/components/InteractiveButton.tsx in Module 3.5's sample-app is a React component.
Used in: Module 3.5 — Error message to file pointer.
react-server-components
An architectural model in React for components that render entirely on the server before being sent to the browser; the default in Next.js App Router. The deeper "why" behind the server/client split that 'use client' toggles; covered in depth in Module 7's where-to-go-next track. Example: a StaticHero.tsx file with no 'use client' directive is a React Server Component.
Used in: Module 3.5 — 'use client' and the server/client split.
repository
A project's full history of commits, tracked by git. Often shortened to "repo." Example: this course is one git repository; you can clone the whole history to your computer with git clone.
Used in: Module 2 — git and GitHub.
request
A structured message asking a server for something — like a paper form handed to a receptionist. Example: GET /api/posts is a request.
Used in: Module 1 — Where data lives, how programs talk.
response
A structured message replying to a request — like the receptionist's paper reply. Example: a JSON array of posts is a response. Used in: Module 1 — Where data lives, how programs talk.
risk-blindness
When an AI agent suggests something dangerous — overwriting working code, dropping a database table, force-pushing to a branch, hardcoding a secret — with the same calm as fixing a typo. The agent has no sense of stakes; it weighs all changes by token-level fit, not by impact on your project. Example: in Module 5's watch-it-fail walkthroughs, the agent proposes deleting a migration file to "clean up" — the operation reads as routine to it but is destructive to the project. The smell-test pattern is taught in those walkthroughs. Used in: Module 2 — AI coding agents.
row
A single record in a database table — like one index card in a filing-cabinet drawer. Used in: Module 1 — Where data lives, how programs talk.
runtime
A program that reads source code and executes it. Every language has at least one. Example: Node is the runtime for JavaScript outside the browser; the browser itself has its own JavaScript runtime built in. Used in: Module 2 — The runtime (Node).
S
schema
The fixed shape of fields in a database table. Example: the users table's schema is (id, email, display_name, created_at).
Used in: Module 1 — Where data lives, how programs talk.
server
A program that runs continuously, waiting for requests, and sends back responses. Used in: Module 1 — Where data lives, how programs talk, Module 1 — How the web works.
server-component
A Next.js file that renders on the server before sending HTML to the browser; the default in App Router. No 'use client' directive needed. Example: app/components/StaticHero.tsx in Module 3.5's sample-app is pure JSX with no interactivity, so it stays a Server Component.
Used in: Module 3.5 — 'use client' and the server/client split.
session
A remembered "yes, you're you" so an app doesn't re-check identity on every request. Lives between authentication and the next sign-out. Example: after you log in, the app remembers you for the next 24 hours. Used in: Module 1 — Who can do what.
session-token
A string the browser sends with each request to prove "I'm the same person who just authenticated." Often delivered as a cookie. Example: a JWT or an opaque session id. Used in: Module 1 — Who can do what.
slash-command
A short keyword starting with / typed inside an AI agent's session to control the session itself rather than asking the agent to do work. Example: /clear resets conversation history; /context shows context-window usage on Claude Code; /stats is Gemini CLI's equivalent.
Used in: Module 2 — AI coding agents.
slash-clear
The /clear slash command — reset the conversation history; start a fresh session inside the same agent invocation. Same keystroke on Claude Code AND Gemini CLI. Example: type /clear between unrelated tasks.
Used in: Module 3 — Planning vs execution conversations.
slash-compact
The /compact slash command (Claude Code) — compress conversation history without losing the gist. Gemini CLI's equivalent is /compress. Example: use mid-session when context-window usage is high but you do not want to /clear and lose recent context.
Used in: Module 3 — Planning vs execution conversations.
slash-compress
The /compress slash command (Gemini CLI) — Gemini CLI's equivalent of Claude Code's /compact. Same purpose, different keystroke. Example: Path 2 learners use this whenever Claude Code learners would use /compact.
Used in: Module 3 — Planning vs execution conversations.
slash-context
The /context slash command (Claude Code) — shows how much of the context window is currently in use. Gemini CLI's equivalent is /stats. Example: type /context to see usage as a percentage or a tokens-used / tokens-remaining pair.
Used in: Module 3 — Planning vs execution conversations.
slash-cost
The /cost slash command (Claude Code) — shows running session spend in dollars. Most relevant to Path 3 (Anthropic API token-careful) learners. Example: type /cost to see spend so far this session.
Used in: Module 3 — Planning vs execution conversations.
slash-stats
The /stats slash command (Gemini CLI) — Gemini CLI's equivalent of Claude Code's /context. Shows conversation statistics including token usage. Example: Path 2 learners use this whenever Claude Code learners would use /context.
Used in: Module 3 — Planning vs execution conversations.
sql
Structured Query Language — the standard way to ask a relational database for rows. Example: SELECT * FROM posts ORDER BY created_at DESC.
Used in: Module 1 — Where data lives, how programs talk.
stack-trace
A list of every function call leading to an error, top to bottom — the most recent call at the top. Most lines mention library code; one or two lines mention YOUR files. Example: Module 3.5 Lesson 3 teaches finding the first line that mentions a file from your project as the file pointer. Used in: Module 3.5 — Error message to file pointer.
steer
The "steer" step of the agent loop — course-correcting when the agent's output does not match your intent. Example: "The date appeared above the tagline; please put it below" is a steer. Used in: Module 3 — Introducing the loop.
T
terminal
The text panel inside a code editor (or as a standalone app) where you type commands and the computer types replies. Example: in a Codespace, the terminal is the panel at the bottom; pressing Ctrl+` toggles it.
Used in: Module 0 — Codespaces walkthrough.
token-discipline
The set of habits that keep AI-coding sessions cheap on pay-per-token plans: clearing context between unrelated tasks, watching the running token count, summarizing long histories, and choosing the smaller model when the bigger one isn't needed. Example: Module 3 teaches /clear, /compact, /context (window usage), and /cost (spend) on Claude Code, and /clear, /compress, /stats as the Gemini CLI equivalents.
Used in: Module 3 — Planning vs execution.
typescript
A version of JavaScript with extra type information. TypeScript files end in .ts; TypeScript files that include React JSX end in .tsx. A separate tool (the TypeScript compiler) checks the types before the runtime runs the code. Example: every file inside Module 3.5's sample-app is a TypeScript file (.tsx).
Used in: Module 3.5 — Reading a file tree.
Used in: Module 0 — Cost-path triage.
U
url
The address that names what you're asking for on the web. Example: https://example.com/about.
Used in: Module 1 — How the web works.
use-client
A Next.js directive — 'use client' on the first line of a file — that flips the file from Server Component to Client Component. Example: a file using useState, onClick, or any other React hook or DOM event handler needs 'use client' on line 1.
Used in: Module 3.5 — 'use client' and the server/client split.
V
vercel
A service that runs your code on the public internet. Watches a GitHub repository, builds the code on every push, and serves it at a public URL. Example: the course platform deploys to Vercel at https://shipyourfirstthing.com.
Used in: Module 1 — How it goes live.