An emitter follower is a type of transistor amplifier configuration that provides high input impedance and low output impedance. It is commonly used to buffer signals, allowing a weak signal to drive a stronger load without significant loss of quality. In this setup, the output voltage closely follows the input voltage, hence the name "follower." In an emitter follower, a bipolar junction transistor (BJT) is typically used, where the input is applied to the base and the output is taken from the emitter. This configuration is beneficial in various electronic applications, such as in audio amplifiers and signal processing circuits, where maintaining signal integrity is crucial.