Context
Everything the AI knows right now in your conversation. Your question, the documents you shared, the chat history, the instructions it was given. Context shapes the answer more than almost anything else.
Context Window
How much the AI can hold in its head at one time, measured in tokens. The newest models can handle a whole book's worth. When AI "forgets" something from earlier in a long chat, it usually ran out of context window.
Context Engineering
The skill of deciding, on purpose, what the AI gets to see. Which documents, which history, which instructions. It's more strategic than prompt engineering, and it's where the best AI results actually come from.
Token
The small chunks AI uses to read and write. About three-quarters of a word. Tokens matter because pricing, speed, and how much the AI can handle are all measured in them.