Transistors are miniature electronic switches. They are the building blocks of the microprocessor which is the brain of the computer. Transisitors have no moving parts and are turned on and off by electrical signals. The on/off (binary) switching of transistors facilitates the work performed by microprocessors.

an on-off switch controlled by high and low levels of electrical currents.

An active semiconductor device capable of providing power amplification. Transistors have three or more terminals.