Core Concepts
Context Window
Also known as: context length
In one line
The maximum amount of text an AI can hold in mind at once.
What does Context Window mean?
The context window is the total tokens an LLM can consider in a single request (prompt + response). Larger windows let you paste more documents but cost more and can dilute focus.
A real-world example
Claude Sonnet 4.5 has a 200K-token window; that's about 150,000 words — roughly a 500-page book.
Related terms
Large Language Model (LLM)
A neural network trained on huge text collections to predict the next word — the engine behind ChatGPT, Claude and Gemini.
Token
The unit of text an AI reads and generates — roughly ¾ of a word.
Retrieval-Augmented Generation (RAG)
A technique where the AI looks things up in your documents before answering.