A special type of receptacle called a GFCI (or GFI), short for ground-fault circuit interrupter, is required in kitchens, bathrooms, and other exposed and/or damp areas of a home to protect from the serious shock that can occur where electricity and water meet.
Identified by the reset and test buttons located on its face, a 120-volt GFCI receptacle takes the place of a standard duplex receptacle and monitors electric current. It is like a super-sensitive circuit breaker. Whenever the amounts of incoming and outgoing current are not equal, such as during a ground fault or current leakage, the GFCI will sense the problem and shut down itself or, in some cases, other receptacles on the same circuit.
So if one or several of the receptacles in the kitchen, bathroom, or outdoor areas ceases to work, look for the GFCI receptacle that serves that circuit.
Just push the reset button to reset the receptacle–this will turn on any others connected to it. Push the test button periodically to ensure that the device is working.