The term "wall plug" has two distinct meanings, one within the context of residential and commercial electrical circuitry and the other in the context of general construction supplies and building materials. An electrical wall plug, also known as an outlet or receptacle, is the point of connection between a pluggable electrical appliance and the circuitry of the building. In terms of construction materials, a wall plug is a plastic or metal sleeve that can hold a screw in a wall that would otherwise not be able to support it.
An electrical wall plug, or receptacle, being the point of use for all pluggable electrical devices, must conform to safety and efficiency standards established by regulating agencies in each country. Wall plug designs vary from region to region throughout the world because no single standard has been adopted for the voltage at which electricity is supplied by power companies. Countries for which 100 to 120 volts is the standard have receptacles with vertical and horizontal slots, while those for which 200 to 240 volts is the standard have round or square holes. In the United States, receptacle design is determined by the National Electrical Manufacturers Association (NEMA), and its designs are used in other North American countries.
In building trades other than those concerning electricity, a wall plug means the same thing as a wall anchor or screw anchor. Certain wall materials like plaster, drywall, and concrete cannot hold screws. When driving a screw into these materials is necessary, the usual procedure is to drill a hole and insert a wall plug to hold the screw. The hole must be just deep and wide enough so the plug will fit tightly when tapped in with a hammer, and the force of the screw being driven in secures it against the sides of the hole.
The amount of weight a screw anchor can support depends upon the material of which it is made and its design. A conical plastic wall plug can hold the least amount of weight and is frequently used to attach lightweight shelving or pictures to drywall and plaster walls. When more holding power is required, a fastener such as a metal screw anchor, a winged or threaded plastic wall plug, or a molly bolt, which flares out at the end as the screw is driven, is usually used instead. A wall plug made of lead is usually employed when it is necessary to drive a screw into concrete.