Terms beginning with F are about controlling risk and rollout — feature flags, failover, fail-fast pipelines and fan-out. Each definition is written to be clear and quotable.
A feature flag is a runtime switch in code that turns a piece of functionality on or off without redeploying. Teams use flags to ship code dark, expose features to a subset of users, run A/B tests, and instantly disable broken features - decoupling deployment from release and shrinking the blast radius of a bad change.