System Prompt
also system message
A system prompt is a top-level instruction that sets a model's role, rules, and behavior before the user's messages are processed.
Analogy
Like the job description and ground rules you give an employee before they start handling customers.
Why it matters
It is where you lock in tone, format, and guardrails for every AI step, keeping automated outputs consistent across runs.
In practice
"You are a polite booking assistant. Only answer using the provided business hours."