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Glossary
Plain-English coding terms with just enough real-world context to keep vibe coders out of the ditch.
10 expanded guides 107 quick definitions Updated May 19, 2026
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200 OK
The request succeeded.
404 Not Found
The server can’t find the requested resource.
500 Internal Server Error
The server had an unexpected problem.
A
A/B test
Show different versions to users to see which performs better.
Accessibility
Design and code so everyone can use your site, including people with disabilities.
Alt text
Text that describes an image for screen readers and slow connections.
API key
API keys are app-to-app credentials. They tell a service which project is making the request, but they are not the same thing as user login.
Argument
The actual value you pass into a function’s parameter.
Array / List
An ordered collection of values.
Astro
A web framework that ships minimal JavaScript by default.
B
Back-end
If the frontend is what people click, the backend is what actually keeps the app honest, stores the data, and talks to outside services.
Boolean
A value that’s either true or false.
Branch
A separate line of work for changes.
Bug
An error that makes software behave unexpectedly.
Build
Process that prepares code for production (bundling, minifying, etc.).
Bundler
Tool that combines many files into a few optimized ones.
C
Cache
Stored results to avoid doing the same work again.
CDN
Servers around the world that serve your static files quickly.
CI/CD
Automation that tests and ships code on every change.
Class
A template for creating objects with the same shape/behavior.
CLI
A command line interface (CLI), also known as a "terminal", is a text‑based interface to run commands.
Client
The device/app that requests and uses data from a server.
Clone
Make a local copy of a remote repo.
Commit
A saved snapshot of your changes with a message.
Component
A self‑contained, reusable piece of UI.
Conditional (if/else)
Run code only when a condition is met.
Constant
Like a variable, but its value cannot change after it’s set.
Cookie
Small data saved by a website in your browser.
CORS
Rules that control which websites can talk to your server.
CSR (Client‑Side Rendering)
The browser renders the page from data using JavaScript.
CSRF
An attack that tricks a logged‑in user into making a request they didn’t intend.
CSS
The visual styling (layout, colors, fonts).
D
Database
A structured place to store and query data.
Debugging
Finding and fixing bugs.
Dependency
Another package or library your project relies on.
Deploy
Deploying is the step where your app leaves your laptop and becomes a real internet thing with URLs, logs, and consequences.
DNS
DNS is the layer that makes your custom domain point at the right hosting platform, email provider, or subdomain target.
DOM
The in‑memory structure of a web page that JS can change.
E
E2E
Short for "End-to-end". Tests the entire app like a real user would.
Endpoint
An endpoint is the address for one API capability. Different endpoints do different jobs, even when they belong to the same service.
Environment variable (.env)
Configuration values (often secrets) set outside your code.
Expression
Code that produces a value.
F
Feature flag
A switch that turns features on/off without redeploying.
Fork
Copy someone else’s repo to your own account to experiment.
Framework
A structured foundation that provides patterns and tools to build apps.
Front-end
Everything users interact with directly on your website or app (i.e. buttons, text, slick animations).
Full‑stack
Working on both frontend and backend.
Function
Reusable code that does a task, often returns a result.
G
Git
The most common version control system.
Glue Code
Glue code refers to small bits of code written to connect different software components, libraries, systems, or APIs that were not originally designed to work together. It's not responsible for the core functionality but rather for bridging gaps, handling conversions, adapting interfaces, or orchestrating data flow between parts of a system. Glue code is common in scripting, automation, and integrating legacy systems or third-party libraries.
GraphQL
An API where clients ask for exactly the data they need.
H
Hosting
Paying a company to keep your website’s files on a server connected to the internet.
HTML
The structure and content of web pages.
HTTP / HTTPS
The protocol for moving data on the web; HTTPS is the secure version.
Hydration
Activating static HTML with JavaScript so it becomes interactive.
I
IDE
Integrated Development Environment. An all‑in‑one code editor with helpful tools.
Index
A data structure that speeds up lookups.
Integration test
Tests how pieces of the system work together.
IP address
A numeric address for a device on a network.
Islands architecture
Mostly static pages with small interactive sections (“islands”).
J
JavaScript
The language that makes web pages interactive.
JSON
JSON is the default language of modern APIs. It is how apps commonly pass structured information back and forth.
JWT
Stands for "JSON Web Tokens", a signed token proving your identity that servers can verify.
L
Latency
How long it takes for a response to start arriving.
Library
Reusable code you can call in your project.
Local storage
Key–value storage inside the browser.
Loop
Repeat a block of code while a condition is true or for each item.
M
Markdown
Plain text with simple symbols for formatting.
Merge
Combine changes from one branch into another.
Method
A function that belongs to an object or class.
Migration
Migrations are how teams change a database safely over time instead of poking production tables by hand and hoping for the best.
Minification
Shrinking files by removing whitespace and short names.
Mock
A fake stand‑in for a real dependency used during tests.
Module
A single file or small bundle of related code.
Monthly Active Users (MAU)
MAU is a simple growth metric that tells you how many real users showed up and did something meaningful in the last month.
N
Node.js
Runs JavaScript outside the browser (on servers or your machine).
NoSQL
Databases that aren’t strictly tables/rows (e.g., documents, key‑value).
npm
JavaScript’s package manager for installing libraries.
Null / Undefined
A special value meaning “nothing here” or “not set.”
Number (int/float)
Numeric data, whole or with decimals.
O
OAuth
OAuth is the thing behind “Continue with Google” and “Sign in with GitHub.” It is about delegated access, not sharing passwords.
Object / Dictionary
A collection of key–value pairs.
Operator
Symbols that do math or comparisons (+, -, >, &&, etc.).
P
Package
A shareable bundle of code (often a library + metadata).
package.json
Project file that lists dependencies and scripts.
Parameter
The placeholder name inside a function for an input value.
Props (properties)
Inputs passed into a component.
Pull Request (PR)
A request to review and merge your code into the main code.
R
Rate limit
A cap on how often you can call an API.
React
A popular library for building UI (user interface) with components and state.
README
A guide in the repo that explains how to use or develop the project.
Refactor
Improve the code’s structure without changing what it does.
Repository (repo)
A project folder tracked by Git, including its history.
Responsive design
Layouts that adapt to different screen sizes.
REST API
A common style of web APIs using URLs and HTTP verbs.
Runtime
The period when your code is actually executing.
S
Schema
A schema says what fields exist, what types they should be, and sometimes what counts as valid data.
Semantic HTML
Using correct tags that describe meaning (e.g., <nav>, <main>).
Server
A computer that’s always on, ready to respond to requests from other computers (a.k.a. clients).
Shell
The language/environment your terminal uses (e.g., bash, zsh).
SPA (Single‑Page App)
A web app that loads once and updates views without full page reloads.
SQL
SQL is how you ask a relational database for exactly the rows you want, change stored data, or define tables and relationships.
SSG (Static Site Generation)
Pages are prebuilt as static files at build time.
SSR (Server‑Side Rendering)
Pages are rendered on the server and sent ready to view.
Stack trace
A report showing which functions were running when an error happened.
State
The current data that drives what a component shows.
Statement
A complete instruction that does something.
String
Text data.
T
Technical debt
Shortcuts that speed you up now but cost more later.
Tree shaking
Removing unused code during the build.
U
Unit test
Tests a small piece of code in isolation.
Uptime
How much of the time a service is available.
URL
The address of a page or resource on the web.
V
Variable
A named container that holds a value you can change.
Version control
Tracks changes to files over time with history and branches.
W
Webhook
A URL you give a service so it can notify your app when something happens.
X
XSS
Stands for "Cross-Site Scripting". An attack where untrusted scripts run in your page.