http://en.wikipedia.org/wiki/Power_socket

AC power plugs and sockets are devices that connect appliances, portable light fixtures, and other electrically-operated devices to the commercial power supply so that electric power can flow to them

Power sockets power receptacles, or power outlets are female electrical connectors that have slots or holes which accept the pins or blades of power plugs inserted into them and deliver electricity to the plugs. Sockets are usually designed to reject any plug which is not built to the same electrical standard. Some sockets have a pin that connects to a hole on the plug, for a ground contact.