The Concept of Wall Sockets

Wall sockets/ electrical outlet plugs are arguably part of the most important things in our daily life that we actually don't pay attention to, and there are currently 15 types of electrical outlet plugs in use today, each of which has been assigned a letter by the US Department of Commerce International Trade Administration (ITA), starting with A and moving through the alphabet. These letters are completely arbitrary: they don’t actually mandate anything.

The work of these electrical outlet plugs is actually to allow electrically operated devices to get connections to an alternating current (A.C.) power in the specific building .
Today there are approximately 20 types in common use around the world, and many obsolete socket types are still found in older buildings.

A plug generally has matching pins so it is known as a male connector, and it is connected by a mains cable (the power cord) or physically built into a piece of electrical equipment that consumes electricity. Some types of socket have male pins and the matching plugs have female contacts, but for safety reasons these are only used for earthing. Some plugs have built-in fuses for safety. Sockets that operate around 240V tend to have built-in switches to avoid arcing when the plug is inserted or removed; sockets that operate around 120V tend not to have built-in switches.

Piling this up, i had little help from the Wikipedia.