An audio amplifier is an electronic device that increases the power of audio signals, making them strong enough to drive speakers. It takes a weak audio signal from a source, such as a microphone or music player, and boosts it so that it can produce sound at a higher volume. Audio amplifiers come in various types, including class A, class B, and class D, each with different efficiencies and sound qualities. They are commonly used in home theater systems, musical instruments, and public address systems to enhance sound clarity and volume for listeners.