Prompt
Also called input, instruction
The text you give an AI model to tell it what to do.
A prompt is everything you send to a language model to get a response. In a chat app it is usually your message, but behind the scenes the full prompt often includes more: a hidden system prompt from the app, earlier messages in the conversation, files you attached, and sometimes search results the app fetched for you.
The model reads the whole prompt as text, split into tokens, and generates a reply that continues it in a likely way. That is why details in the prompt have so much effect. The model has no other source for what you want: not your goals, not your audience, not what you tried yesterday, unless that information is in the prompt or in memory the app adds to it.
A useful prompt usually answers five questions: what is the task, what context does the model need, what are the constraints, what should the output look like, and how will you judge a good answer. Not every prompt needs all five, but a weak result can usually be traced to one that is missing.
Example
"Write a bio" gives a generic paragraph. "Write a 60-word bio for my conference speaker page. I am a nurse turned health-tech founder. Audience: hospital IT buyers. Third person, no buzzwords" gives something you can use.
Common mistake
Assuming the model remembers context it does not have. A new chat usually starts with no knowledge of your earlier chats, unless the app has a memory feature turned on. If an answer seems to ignore something obvious, check whether that something was actually in the prompt.