Prompt
The text you send an AI model to get it to do something — a question, an instruction, or a task with its data.
A prompt is the input you give a language model: the question, instruction, or task you want it to act on. Everything the model produces is a response to that text, so the prompt is the single biggest lever you have over the quality of the output.
In a chat app you type a prompt into a box. In an application, the prompt is assembled in code — often a stable system prompt plus the user's request plus any data you retrieved. Either way, the model only knows what the prompt tells it: it cannot see your intent, your audience, or the context in your head unless you write it down.