A GFCI outlet, or ground-fault circuit interrupter, is an outlet that stops electricity from flowing through it if it detects a problem or a ground-fault. The outlet trips, the same as a breaker trips in an electrical panel, as a safety measure.
Ground-fault circuit interrupter outlets are installed in areas where water is present, such as a kitchen or bathroom. If a faulty tool or appliance is plugged into the outlet, it trips the outlet to protect a person from electrical shock. A person can still experience a shock, but not a deadly one.
GFCI outlets can come in the form of a receptacle outlet, portable outlet or built in to the cord of a device. Each outlet features a red "test" button and black "reset" button.