What are plugs?

Some articles on plugs, plug:

Core Plug
... Core plugs, also known as Welch plugs, are metal discs that fill the sand casting core holes found on water-cooled internal combustion engines ... They are often wrongly called Welsh plugs, frost plugs or freeze plugs ... The core plug is a thin, domed, disc of ferrous metal which is pressed into these holes ...
Sexual Dimorphism In Non-human Primates - Ultimate Causes - Copulatory Plugs
... Copulatory plugs are a passive form of mate guarding, which reduces selection pressure for a larger male size ... In species where copulatory plugs are present there is a smaller degree of sexual dimorphism ...
Coaxial Power Connector - Common Sizes and Interchangeability
... The most common plugs are 5.5 mm in outside diameter (OD) and 9.5 mm in length ... Two inside diameters (ID) are common in the plugs for this size, 2.1 mm and 2.5 mm, and ideally the pin in the jack should match ... Generic plugs are often named after the inside diameter, so these types will be seen described as 2.1 mm DC plugs and 2.5 mm DC plugs respectively ...
Test And Tagging - Testing - Polarity Check - Plugs
... The order (polarity) of the pins of a three pin flat pin plug, to their connections, shall be Earth (radial pin – green/yellow wire), Neutral (light blue wire) and then Active (brown ...
British Telephone Sockets - Plugs
... There are two types of modern British Telecom plugs – 431A and 631A ... There are also plugs with only two contacts commonly seen on modem leads ... These closely resemble standard 631A connectors but the keying slots on the back of the plug have a different size and position ...