Claude Code is Anthropic's AI assistant that runs inside VS Code or your terminal, reads files, runs commands, and connects to external services through MCP. This glossary defines the 24 terms you will hit in your first week. Written in plain English, no developer background needed.
Most people who pick up Claude Code for the first time hit a wall within ten minutes. Not because it is hard, but because every explanation assumes you are a developer.
You are not. But you have heard enough about Claude Code to be curious, and you are not the type to sit still while everyone else figures it out first.
This is the reference post I wish had existed when I started.
It will not turn you into a developer. It will make sure you understand what is being talked about when people throw around terms like MCP, hooks, or subagents. And it will show you what Claude Code actually is for someone in your seat.
What is Claude Code, really?
Claude Code is a version of Claude that lives inside your code editor (VS Code) or runs directly in your terminal. Unlike Claude.ai in your browser, it reads and writes files, runs commands, searches your folder structure, and connects to external services. It does not just answer questions. It does things.
For developers, that means writing and testing code. For everyone else, it means having an AI that works in your files and across your tools, not just in a chat window you copy-paste from.
The difference: Claude.ai is a conversation. Claude Code is a colleague who has access to your drives and calendar and goes builds the thing, not just advises on it.
Which Claude Code terms come up most often?
The glossary below covers 24 terms grouped alphabetically. Each entry answers one question in 40 to 80 words. Read top to bottom, or jump to the letter you need.
What is an agent in Claude Code?
An agent is a specialised version of Claude you call for a specific job, running in parallel with your main conversation. Your main Claude handles the conversation. The agent runs a dedicated task in the background: writing a summary, checking a file, updating a record. You set the rules; the agent does the work.
What does AGENT.md do?
AGENT.md is the instruction file for an agent. It tells the agent what to do, which tools it can use, and what to avoid. You write this once and it applies every time that agent runs. Closer to a job description than a prompt.
What is a branch in Git?
A branch is a separate version of your files that runs alongside the main one. You make changes there, check that they work, and merge them back in. Nothing breaks until you choose to apply it. Most Claude Code work happens on branches, not directly on the main line.
What is Claude Code?
Claude Code is Anthropic's AI assistant that runs inside VS Code or your terminal. It reads files, runs commands, searches your folder structure, and connects to external services through MCP. Different from Claude.ai in your browser: Claude Code does the work in your files, not just in a chat window. The rest of this glossary describes the parts that make it work.
What does CLI mean?
CLI stands for Command-Line Interface. You control a CLI by typing commands instead of clicking menus. Examples: git status, npm install, gh pr create. Claude Code uses the CLI heavily. You do not need to master it yourself, but knowing it exists explains a lot of what you see.
What is CLAUDE.md?
CLAUDE.md is the instruction file Claude Code reads at the start of every conversation. It tells Claude who you are, what the project is, which rules apply, and where to find things. Not a knowledge dump, a map. One of the most useful files you set up.
What is a commit?
A commit is a saved snapshot of your work with a message explaining what changed. Like a version in document history, but intentional: you decide when to commit and what to write. "Updated homepage copy" or "Fixed broken link in nav". Small frequent commits beat one big commit at the end.
What is the context window?
The context window is the amount of text Claude holds in mind at once. Not infinite. When a conversation gets very long, earlier information drops out. Think of it as working memory. If Claude starts forgetting things you said earlier, you have hit the limit. Starting fresh, or keeping instructions in CLAUDE.md, solves this.
What is a draft in Claude Code output?
A draft is what Claude produces on a first pass. Treat it as work from a smart colleague who has not read everything twice. Check it before you use it. The quality of the output depends on the quality of the input, which is your prompt plus your CLAUDE.md context.
What is a VS Code extension?
An extension is a plugin that adds functionality to VS Code. Claude Code runs as an extension inside VS Code, which is why you use it without leaving your editor. You install it once from the VS Code marketplace and it stays connected to your workspace.
What is Git?
Git is the version control system that tracks changes to your files over time. It keeps full history, lets you go back, and makes it possible for multiple people to work on the same project without overwriting each other. Claude Code uses Git constantly in the background. You do not need to learn all of it, but it explains the terms branch, commit, push and pull.
What is a hook in Claude Code?
A hook is an instruction that runs automatically when something happens. Example: every time Claude Code starts a session, run git pull to make sure you have the latest version. You set up hooks once and they fire without you thinking about it. Good for routine tasks you would otherwise forget.
What is INDEX.md?
INDEX.md is a short file that describes what is in a folder. It helps Claude (and you) find things without reading every file. Maintained automatically by the index-builder skill, not something you update by hand. Keep it under 200 lines.
What does MCP stand for?
MCP stands for Model Context Protocol. It is the standard that lets Claude talk to external services: your calendar, task manager, email, or internal tools. Each service runs as an MCP server, and Claude picks up tools from it. When someone says "I connected Claude to ClickUp", that is MCP under the bonnet.
What is MEMORY.md?
MEMORY.md is an index of persistent notes Claude carries between conversations. Not the notes themselves, just the list of what exists and where. This means Claude remembers your context, preferences and ongoing projects without you having to re-explain everything each session.
What is permission mode?
Permission mode controls how strict Claude is about asking your approval before doing things. On strict settings, Claude asks before every file write. On looser settings, it works more autonomously. You choose the balance based on how much you trust the setup and what the task involves.
What is plan mode?
Plan mode is a setting where Claude shows you what it intends to do before doing it. Useful for anything non-trivial. Claude presents the plan, you approve or adjust, then it executes. Catches misunderstandings before they become file changes.
What is a good prompt for Claude Code?
A good prompt is short and contextual. "Write a summary of this meeting in three bullet points for a non-technical audience" beats a paragraph about why you need it and what you have tried before. Claude already knows a lot from CLAUDE.md. Use your prompt for the specific job at hand.
What is a pull request (PR)?
A pull request is a formal proposal to merge changes from one branch into another, usually reviewed before it goes through. Common in teams working on shared files. If you ever see "can you review my PR", this is what they mean. Created with gh pr create from Claude Code.
What is a remote in Git?
A remote is the copy of your files stored outside your computer, usually on GitHub. Your local files are what you work in. The remote is the backup and the shared source. push sends local changes to the remote. pull brings remote changes to your local copy.
What is a repository (repo)?
A repository is a project folder with full version history attached. Everything that has ever been committed is still there, traceable. Your repo is what Claude Code works in. One workspace, one repo, usually.
What is a shell?
A shell is the programme that interprets the commands you type in a terminal. On Windows that is PowerShell. On Mac and Linux that is Bash. The terminal is the window. The shell is what understands what you type. Different shells use different syntax, which is why some commands look different across systems.
What is a skill in Claude Code?
A skill is a reusable instruction set you call by typing /name. Each skill does a specific job: writing a LinkedIn post, summarising a document, checking your calendar. Skills run in your main conversation and follow the same rules as everything else. Think of them as shortcuts to predefined workflows.
What is a slash command?
A slash command is a command that starts with /. It calls a skill or a built-in function. Examples: /news, /reflect, /task. Fast way to trigger a workflow without writing a full prompt. Type / in Claude Code and you see the available list.
What is a system prompt?
A system prompt is the fixed instructions an agent or version of Claude receives at the start of every session. It sets the role, the tone, the constraints. You usually do not see it, but it shapes everything. CLAUDE.md feeds into the system prompt for your workspace.
What is the terminal?
The terminal is the window where you type commands. In VS Code you open it with Ctrl+`. The terminal itself is just the window. The shell is what runs inside it and interprets what you type. On a Windows workspace the default shell is PowerShell.
What is a workspace in VS Code?
A workspace is the root folder VS Code and Claude Code consider your working environment. Everything within it is accessible to Claude. Everything outside it is not, unless you explicitly give access. Your workspace is where CLAUDE.md lives, which means it is where Claude's instructions live.
What does this actually mean for you?
You do not need to understand all of this to start using Claude Code. You need to understand enough to have a conversation with someone who does.
The terms above come up constantly. Knowing what a hook is, why the context window matters, or what the difference is between a skill and an agent, saves you from nodding along while someone explains their setup.
More practically: Claude Code is not a developer tool that happens to be useful for other people. It is a system for giving AI access to your actual work, with guardrails you define. That is useful whether you write code or not.
The people getting the most out of it are not the most technical. They are the ones who set up CLAUDE.md properly, think about what context Claude actually needs, and decide which tasks are worth automating and which are not.
When you are ready to move beyond a glossary into a real working setup, the BUILD framework gives you the five steps to create your first AI team member: pick the task, write the rules, gather the knowledge, lay out the instructions, debug until it works. The frame applies whether you use Claude Code or a Custom GPT.
Frequently asked questions
Do I need to know how to code to use Claude Code?
No. Claude Code is built for technical work, but most of the value for a non-developer comes from setting up CLAUDE.md, configuring agents and skills, and connecting MCP servers. None of that requires writing code yourself. You write instructions in plain English (or Dutch), and Claude executes them.
How is Claude Code different from Claude.ai?
Claude.ai runs in your browser and only answers questions. Claude Code runs inside VS Code or your terminal and reads files, writes files, runs commands, and connects to external services through MCP. The difference is access. Claude.ai is a conversation. Claude Code does the work.
What is the first file I should set up in Claude Code?
CLAUDE.md, in the root of your workspace. It tells Claude who you are, what the project is, what rules apply, and where to find things. A good CLAUDE.md is a map, not a knowledge dump. Without it, Claude works in the dark. With it, every session starts with shared context.
Can Claude Code connect to my calendar, email, or task manager?
Yes, through MCP servers. Common integrations include Google Calendar, Gmail, ClickUp, Notion, and GitHub. Each integration runs as a separate MCP server you configure once. After that, Claude picks up tools from those servers and uses them in your conversations. You control which services are connected.
Is Claude Code safe to use on confidential work?
It depends on your setup. Claude Code runs locally and only sends what you tell it to send. Permission mode controls what gets approved before execution. MCP servers run with your credentials. Confidential work is fine on a properly configured setup. Read the security guidance before you connect production systems.
This glossary was assembled by Guus Witjes at Step Ahead AI, based on six months of running Claude Code as a daily tool across HAN University's Digital Marketing team and his own consulting work.