Plug and socket outlet 
A device for the frequent coupling between a flexible cable and an electric circuit; it consists of a socket outlet and a plug.

Socket-outlet 
The part designed to be connected to the electric circuit.

Plug
The part fixed or designed to be fixed to the end of a flexible cable, which is attached to an appliance or to a connector.

Cable coupler
A device for the frequent coupling between two flexible cables; it consists of a connector and a plug.

Connector 
The part fixed or designed to be fixed to the end of a flexible supply cable.

Appliance coupler 
A device for the frequent coupling between a flexible cable and the appliance, it consists of a connector and an appliance inlet.

Appliance inlet
the part built into or fastened to the appliance, or designed to be fastened to it.

Flexible cable extension
a flexible cable with a connector at one end and a plug at the other.

Industrial and multiphase plugs and sockets
Provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase system, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug. Some types of connectors are approved for hazardous areas such as coal mines or petrochemical plants, where flammable gas may be present.

Almost all three-phase power plugs have an earth (ground) connection, but may not have a neutral because three-phase loads such as motors do not need the neutral. Such plugs have only four prongs (earth, and the three phases).