A “Ground Fault Circuit Interrupter” outlet is a special receptacle that provides a safety mechanism to prevent any of us from electric shock. A GFCI receptacle will sense the current flow into the outlet and the current flow out of the outlet. These 2 should match each other – if they do not, there is a “leak” in current, which will most likely run through the person as a shock. In this case, the GFCI outlet will immediately trip to eliminate this shock hazard.  For more information read the article GFCI Outlet Explained.