Glossary

A plain-language reference for the terms used throughout this book. Each definition is one line and aimed at a beginner — enough to recognize the word when the AI uses it, not a full computer-science course. Technical acronyms are kept in their original form and explained.

Web & APIs

API (Application Programming Interface) : A menu of requests one program offers to another, with rules for how to ask and what you get back.

REST : A common, simple style of API that uses ordinary web addresses and a few standard actions (get, create, update, delete).

endpoint : A single item on an API menu — one URL that does one specific thing.

JSON (JavaScript Object Notation) : A simple text format for data, made of labeled fields and lists, that programs use to talk to each other.

HTTP / HTTPS : The language browsers and servers use to exchange web pages and data; HTTPS is the encrypted, secure version.

status code : A three-digit number a server sends back to say what happened (200 = OK, 404 = not found, 500 = server error).

URL (Uniform Resource Locator) : A web address — the full path that points to a specific page, file, or endpoint.

DNS (Domain Name System) : The internet's phone book that turns a human name like example.com into the numeric address of a server.

domain : The human-readable name you own and type in (like example.com) that points to your site.

webhook : A reverse API call — another service pings your app automatically when something happens, instead of you asking repeatedly.

OAuth : A standard way to let users log in with another account (like "Sign in with Google") without sharing their password.

session / JWT : How a server remembers you're logged in between requests; a JWT is a signed token that carries that proof.

rate limit : A cap on how many requests you can make in a time window, used to stop abuse and overload.

idempotent : An operation safe to repeat — doing it twice has the same effect as doing it once (so a retry can't double-charge).

Code & Tools

frontend : The part of an app you see and click — what runs in the browser or on screen.

backend : The part of an app you don't see — the server code, logic, and data behind the scenes.

CLI / terminal : A text-based way to run commands by typing, instead of clicking buttons in a window.

shell : The program inside the terminal that reads your typed commands and runs them (e.g. bash, zsh).

Git : A tool that tracks every change to your code so you can review history and undo mistakes.

commit : One saved snapshot of your code in Git, with a short note describing what changed.

branch : A separate line of work in Git where you can make changes without affecting the main version.

pull request (PR) : A proposal to merge one branch's changes into another, where they can be reviewed first.

repository (repo) : The folder Git tracks — the home of your project's code and its full history.

.gitignore : A file listing things Git should not track or upload, like secrets and generated junk.

package : A reusable chunk of code, written by someone else, that you add to your project instead of writing it yourself.

dependency : A package your project relies on to work; your code depends on it being present.

lockfile : An auto-generated file that pins the exact versions of every package, so builds are repeatable.

framework : A pre-built foundation that handles common app plumbing so you only write the parts unique to your project.

LSP (Language Server Protocol) : A standard that lets editors offer smart features (autocomplete, error squiggles) for any programming language.

Infrastructure

database : An organized store for your app's data that can be searched, updated, and kept safe over time.

SQL : The classic query language for talking to traditional table-based databases.

NoSQL : A family of databases that store data more flexibly than rigid tables (documents, key-value, etc.).

environment variable : A setting fed to your app from outside the code, often used to switch behavior between local and live.

secret : A sensitive value (password, API key) that must never appear in your code or be shared publicly.

edge : Servers spread around the world close to users, so responses arrive faster.

serverless : A model where your code runs on demand and you don't manage any servers — the provider handles that.

container : A lightweight, self-contained package of your app plus everything it needs to run identically anywhere.

VM (virtual machine) : A full simulated computer running inside a real one, giving you an isolated server to control.

deploy : To publish your app so real users can reach it on the internet.

CI/CD (Continuous Integration / Continuous Delivery) : Automation that tests your code and ships it whenever you push changes.

cache : A temporary fast store of results so repeated work doesn't have to be redone, making things faster.

queue : A waiting line for tasks, so work piles up safely and gets handled one at a time in order.

AI & Agents

MCP (Model Context Protocol) : A standard that lets an AI assistant plug into outside tools and data sources in a uniform way.

agent : An AI that doesn't just answer but takes actions in steps — running tools, reading files, fixing its own mistakes.

prompt : The instructions you give an AI; clearer prompts get better results.

token : The small chunk of text (roughly part of a word) that AI models read and count; usage and cost are measured in tokens.

context window : The maximum amount of text an AI can keep in mind at once; go over it and earlier details get dropped.

hallucination : When an AI states something false but confidently, as if it were a fact.

Payments & Business

merchant of record (MoR) : A company that sells on your behalf and handles taxes, fraud, and refunds, so you don't have to register everywhere.

bill shock : An unexpectedly huge invoice from a cloud or AI service, usually from a runaway loop or missing limit.