The fastest possible "is it fundamentally working?" check after a change or deploy — a handful of key actions against the live system, minutes not hours. Named for switching on a machine and checking for smoke.
Why it matters: the minimum dignity of shipping: never announce "deployed" without one. For AI systems, the best smoke test is a few golden set questions against production — real answers, real data, right now.
---
Related: Golden set
More in “Keeping it running in the real world”