Definition
A feature flag (also called a feature toggle) is a runtime configuration value that determines whether a piece of code is active. Rather than deploying a new version of your software to turn a feature on or off, you flip a flag and the change is instant. Feature flags are used for gradual rollouts, A/B testing, emergency kill switches, and - in SaaS - gating premium features behind a paid plan.
There are several common types of feature flag: release flags (turn new code on), experiment flags (A/B test variants), ops flags (kill switches for production safety), and permission flags (gate by customer tier or role). Good flag systems support targeting rules (enable for users where plan = 'agency'), analytics (track which flags fire in which sessions), and cleanup workflows (retire flags when they are permanently on).
How SheetLinkWP relates to Feature Flag
Each premium feature in SheetLink Forms sits behind a permission-style feature flag that reads from the cached license entitlement. When PHP code wants to know whether to render a premium UI element or register a premium hook, it calls SheetLink_License::can('two_way_sync') or similar. The result is cached with the entitlement for 12 hours, so the check is instant. Disabled features simply do not register - nothing renders, nothing fires, no performance cost.