What is the meaning of Plug-in?

Designed to be plugged into an electrical power outlet or circuit.

Able to be extended with further components in a modular fashion.

Anything that plugs into something.

A module or device that interacts with another to add a specific feature or function.

An electric vehicle that can be recharged from an external power source.

An air freshener that can be charged by connecting it to the mains power supply.

Source: wiktionary.org