Backend & systems·Deployment, release and rollback
you flip the flag and users start getting the new behaviour, on code that has already been running in production for a week.
Release
Exposing new behaviour to users. Separating it from deployment is the single highest-leverage change to a delivery process: deploys become routine and releases become a business decision with an instant off switch. It requires the code to be flag-guarded and both paths to be tested.