A piece of solid material fitting tightly into a hole to block it. Also an electrical connector, or an informal promotion of a product or service.
From Middle Dutch plugge meaning "a peg, plug," possibly from Proto-Germanic. The electrical sense dates from the 1880s when electric plugs were invented.
A plug blocks a hole, connects a power source, and promotes a product. In every case, it makes a connection between two things that need each other.
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