Feature Flag
In plain terms
A switch that turns features on or off without redeploying code.
Going deeper
Feature flags let teams ship code dark, then enable it for some or all users, enabling gradual rollouts, A/B tests, and instant kill switches. They decouple deploy from release.
Under the hood
Enables trunk-based development and progressive delivery, but flags accumulate as technical debt and must be cleaned up; some need server-side evaluation for security.
Examples
LaunchDarkly, Unleash, gradual rollouts, kill switches, A/B experiments.
Think of it like...
Like a dimmer switch wired in during construction: you can turn a room's lights on later, for some guests first, without rewiring the house.