A "GFCI" is a Ground Fault Circuit Interrupter.
This is picture of an outlet version. Some other versions are breakers in the electric panel, separate plug-type, or stand alone. A ground fault circuit interrupter is an inexpensive electrical device that, if installed in household branch circuits, could prevent over two-thirds of the approximately 300 electrocutions still occurring each year in and around the home. Installation of the device could also prevent thousands of burn and electric shock injuries each year.
The GFCI is designed to protect people from severe or fatal electric shocks Because a GFCI detects ground faults, it can also prevent some electrical fires and reduce the severity of others by interrupting the flow of electric current. Where are they needed? General standards say within 6 feet of a water source, outdoors, unfinished basements, and garages. How many do you have? Get great info about GFCI's here.