The context window is the model input space for one request. It can contain your latest message, earlier chat turns, system instructions, retrieved documents, tool results, and sometimes images or other data.
In practice
A larger context window lets an AI system work with more information at once. That is useful for long documents, codebases, research sessions, and multi-step conversations.
What to watch
More context is not always better. Irrelevant or conflicting context can distract the model, increase cost, and make answers harder to control.