A plug on a piece of electrical equipment is a small plastic object with two or three metal pins which fit into the holes of an electric socket and connects the equipment to the electricity supply.

A plug is an electric socket.

A plug is a thick, circular piece of rubber or plastic that you use to block the hole in a bath or sink when it is filled with water.

A plug is a small, round piece of wood, plastic, or wax which is used to block holes.

If you plug a hole, you block it with something.

If someone plugs a commercial product, especially a book or a film, they praise it in order to encourage people to buy it or see it because they have an interest in it doing well.

If someone in a position of power pulls the plug on a project or on someone's activities, they use their power to stop them continuing.