A power amplifier is an electronic device that increases the power of an input signal so it can drive output devices like speakers or radio transmitters. It amplifies low-power signals to a higher power level needed to power external devices. Power amplifiers are used to boost signals to a level sufficient for driving loads such as speakers or transmitting antennas.

2.  A Power amplifier is an electronic amplifier
designed to increase the power of a given input
signal.
 The power of the input signal is increased to a
level high enough to drive the loads of output
devices like speakers, RF Transmitter, etc.,