The text or instructions you give a language model to request a task, such as a question or a description of an app to build.
A prompt is whatever you write to the model: a question, a request or a detailed description of what you want. It can be one line, like summarize this email, or several paragraphs describing a full app idea, its target users, the screens you need and how customers pay.
In AI app builders, prompt quality directly shapes output quality. A vague description produces a generic app that needs many corrections, while a clear one that names the audience, the goal and the constraints gets you much closer to the right version on the first try.
Practical tip: write a prompt that answers four questions: who is it for, what problem does it solve, what are the three most important screens, and what must never happen? Start with a simple version and improve it with short follow-up requests.