Definition
Plain language
Hidden instructions placed at the start of a conversation that shape how the model behaves.
As stated in the literature
A prompt segment, often invisible to end users, that sets persistent context, persona, or behavioral constraints for an LLM session.
Also called: system prompts
Why it matters: It is the main lever developers have for shaping model behavior in deployment, and a major target for prompt-injection attacks.
For example, a customer-service bot might have a hidden system prompt telling it 'You are an airline agent; never discuss competitors.'
Heard on the show
“The AI reads it the way it reads its own system prompt.”Episode 208 — The Blank Space in Your AI Approval Box That Isn't Empty