Final answer:
An emitter follower is a transistor configuration used in applications like audio amplifiers; it can be considered a power amplifier or a current attenuator but not a voltage amplifier or power supply.
Step-by-step explanation:
The emitter follower is a transistor configuration where the voltage applied to the base acts as a control valve for the current flowing from the emitter to the collector. It is commonly used in audio amplifiers where a weak signal from a microphone's movement, modulated by sound waves, is fed into the base to control a larger current that drives a loudspeaker, thereby amplifying the sound. Despite the terminology 'emitter follower', this configuration is not a voltage amplifier since it does not substantially increase the input voltage level. Nor is it a power supply, because it doesn't generate power on its own. Instead, due to its ability to source significant current while maintaining the input signal's voltage, it can be considered either a power amplifier or a current attenuator, depending on the context of its application within the circuit.