Glossary

New to Claude Code? This page defines every term you'll encounter, in plain English. No jargon assumed.

Core Concepts

Claude Code

A command-line tool (CLI) that lets you work with Claude AI directly in your terminal. Unlike ChatGPT which lives in a browser, Claude Code runs where developers work: alongside your code, files, and tools.

CLAUDE.md

A markdown file at the root of your project that tells Claude Code how to behave. Think of it as a "rules of the house" document. It defines your coding standards, communication preferences, and workflow patterns. Claude Code reads it at the start of every session.

Session

One conversation with Claude Code, from start to finish. When you open Claude Code and start working, that's a session. When you close it, the session ends. Without memory, each session starts from scratch.

Context Window

The amount of information Claude Code can "see" at once. Think of it as working memory. Larger context = more files and history it can consider, but also more expensive.

Prompt

What you type to tell Claude Code what to do. Can be a question, a task description, or a command. Better prompts = better results.

Memory & Persistence

Memory System

A file-based system that lets Claude Code remember things across sessions. Without it, every conversation starts cold. With it, Claude Code knows your projects, preferences, and past corrections.

Handoff

A document written at the end of a session that captures what was done, what decisions were made, and what's next. The next session reads this to resume context. Like leaving a note for your future self.

Product Brain

A directory of living project documents that track each project's purpose, progress, and problems. Updated after meetings and decisions. The source of truth for your work.

Automation & Extensibility

Skill

A reusable workflow encoded as a markdown file. Instead of explaining a multi-step task every time, you write a skill once and trigger it with keywords. Example: a "meeting prep" skill that pulls context before any meeting.

Hook

A script that runs automatically at specific moments: before a tool runs (PreToolUse), after a tool runs (PostToolUse), or when a session starts (SessionStart). Like automation rules that fire without you remembering.

Sub-Agent

A separate Claude Code instance that handles a focused task. Your main conversation delegates work (research, code review, testing) to agents that work independently and report back. Keeps your main session clean.

MCP (Model Context Protocol)

A standard for connecting Claude Code to external tools like GitHub, Slack, Jira, and databases. Think of MCP servers as plugins that give Claude Code access to your other tools.

MCP Server

A small program that translates between Claude Code and an external service. Each server gives Claude Code specific abilities (e.g., "read GitHub PRs" or "search Slack messages").

Plans & Pricing

Claude Pro

The $20/month plan. Gives you access to Claude Code with moderate daily usage. Good for getting started and light-to-medium use.

Claude Max

The power user plan. $100/month (5x usage) or $200/month (20x usage). For people who use Claude Code as their primary work tool.

Tokens

The unit that measures how much Claude Code reads and writes. Roughly 4 characters = 1 token. Your plan has a daily token budget. Bigger context windows and longer conversations use more tokens.

Rate Limit

When you've used your daily token allocation and Claude Code slows down or pauses. A sign you might need to upgrade your plan, or optimize how you use context.

Workflow Concepts

Plan Mode

A mode where Claude Code thinks before acting. Instead of immediately writing code, it outlines the approach first for your review. Saves tokens and prevents wrong-direction work.

Autonomous Loop

Claude Code running a task without your direct input, finishing, and automatically starting the next iteration. Advanced pattern for repetitive tasks like fixing tests or scanning for issues.

Orchestration

The rules that govern how Claude Code approaches work: when to plan first, when to delegate to agents, when to verify results. Defined in your CLAUDE.md.

File Types

.claude/

A hidden directory in your project that contains Claude Code configuration: settings, hooks, skills, and agent definitions.

MEMORY.md

The index file for your memory system. Lists all memory files with one-line summaries. Claude Code reads this to know what memories exist.

.mcp.json

Configuration file that defines which MCP servers Claude Code should connect to and their credentials.

settings.json

Claude Code's configuration file. Lives in .claude/settings.json. Defines hooks, permissions, and tool settings.