You will (hopefully) find GFCI outlets in the kitchen and bathrooms. It stands for Ground Fault Circuit Interrupter. GFCIs are there to protect you from being electrocuted by interrupting the circuit when there is a difference in the currents in the hot and neutral wires. The difference indicates that some of the current has found another path. Instead of returning through the neutral wire, current is either traveling through the ground wire or through you if you come in contact with the hot wire or you drop an appliance into water. If you start to get electrocuted, the power should cut off within a few milliseconds, before you get injured . They also help prevent electrical fires.
Many older homes do not have these installed or only in some areas. To provide a greater level of safety, GFCI outlets are now installed in garages and all wet areas, such as near kitchen sinks, laundry tubs, swimming pools, and exterior walls.
Resetting. Often one GFCI protects several outlets so if your outlet is not working, it may not be broken as some friends of mine thought. Check the other bathrooms, garage or even the electrical panel, to find the reset button.
As a Circuit Breaker
Newer houses usually have a GFCI circuit breaker in the electrical panel and it protects all the outlets on that circuit.
Are they required? In south Florida, there is no law that says you must install them if you do not have them, however GFCIs are a wise safety precaution.