Canary Release
Shipping a change to a small slice of production traffic first, watching for regressions, before rolling it out to everyone.
A canary release routes a small percentage of real traffic (often 1–5%) to a new version while the rest keeps hitting the stable one, then watches error rates and latency on that slice before deciding to ramp up or roll back. The name comes from the "canary in a coal mine" — a small, contained exposure meant to surface danger before it reaches everyone.