Feature Flag

A feature flag is a switch in the code that turns a capability on or off — for specific groups of users — without redeploying the code.

A feature flag separates 'shipping the code' from 'activating the capability': the code can be on the server while the capability stays off until the team decides when and for whom to turn it on. That separation makes the flag the shared infrastructure of gradual rollouts, A/B tests and quickly killing a broken capability. But flags create technical debt: each flag is a branch in the code, and forgotten flags turn it into a maze of conditionals, so temporary flags should be removed after the final decision. A flag is not itself an experiment; it is only the mechanism experiments and rollouts ride on.