What is the meaning of Solenoid?

A coil of wire that acts as a magnet when an electric current flows through it.

An electromechanical device consisting of such a coil containing a metal core, the movement of which is controlled by the current.

An electromechanical switch controlled by a solenoid; solenoid switch, relay.

The region of intersection between isobaric and isopycnal surfaces.

solenoid

Source: wiktionary.org