Glossary
GFCI outlet
A ground-fault circuit interrupter outlet that cuts power the instant it senses leaking current.
A GFCI, or ground-fault circuit interrupter, is an outlet or breaker that constantly compares the current flowing out to a device against the current flowing back. If it senses even a small imbalance, which usually means current is leaking somewhere it should not, such as through water or a person, it cuts power in a fraction of a second.
Garages are considered a damp or wet-adjacent location in most electrical codes because they see hoses, wet tires, spilled coolant, and doors left open in rain, so GFCI protection is required there in most jurisdictions. It protects against a specific kind of danger that a standard breaker does not catch, since a normal breaker only trips on overload or a short, not on a small current leak.
GFCI outlets have a test and reset button on the face and should be tested periodically, since the internal sensing components can wear out over years of use even if the outlet still supplies power. A GFCI that trips repeatedly with no obvious cause is often a sign of a tool, cord, or the outlet itself developing a fault, and is worth having checked rather than just resetting and ignoring.