A plug is:

• a device which is designed to stop a fluid from flowing through a hole.
• a mains power plug or other type of electrical connector that mates with a socket or jack, in particular used with electrical or electronic equipment or appliances (See Domestic AC power plugs & sockets.)
• in the entertainment industry, a type of promotion, usually by mentioning one's product during a show
• a way of planting seedlings. See Plug (horticulture).

In electronics, deciding which of two mating connectors is the plug and which the socket is sometimes arbitrary. In general:

• The male connector is the plug, the female the socket. This may pose a problem if both connectors have some male and female characteristics, for example the XLR3.
• The connector possessing the pins is the plug, the other the socket. This may pose a problem if both connectors have pins, for example the European 3-pin power connector.
• The connector normally mounted on a cable is the plug, and the connector mounted on the equipment is the socket. See DC plug for an example of this usage. This may pose a problem if the usage changes with time.

There are also hermaphrodite connectors, see electrical connector.

For the 1990s record producer who goes by Plug, see his other performing name, Wagon Christ.