Hidden instructions an AI app gives the model before your conversation starts.
A system prompt is a set of instructions the makers of an AI app put in before you type anything. It sets the AI's role, tone, rules and available tools. You usually can't see it, but it typically sits at the start of the context window for the whole chat.
The same model can become a homework helper or a language-practice partner depending on its system prompt. Features that let you save standing instructions, like "always answer briefly", work in a similar way.
It isn't a locked safe, though. In 2023, clever prompts got a search chatbot to reveal its hidden instructions.
Think of it like this
Imagine your teacher leaving a note for the substitute: "Take attendance first, and check the homework." You never see the note, but the whole class follows it.
For example
"You are a math tutor for middle schoolers; give hints before answers" is a simple system prompt.
Records about this
Source-checked moments from AI history.
Publicly demonstrated that in a live service the system prompt does not work as a line of defense