Transistor

Controls the movement of electricity by acting as a switch or amplifies electrical signals. There are many variations of transistors including bipolar junction, field effect, photoconductive, metal oxide semiconductor, varactors, etc. Transistors typically have three leads: emitter, base, and collector. The base acts as a switch, controlling whether there is a connection between emitter and collector. Rapidly switching transistors on and off can control the current going to a component.

References:

https://www.electronics-tutorials.ws/category/transistor

https://www.thoughtco.com/what-is-a-transistor-2698913

https://www.explainthatstuff.com/howtransistorswork.html