An amplifier is an electronic device that increases the power of audio signals to drive speakers or headphones. Audio amplifiers work by taking a weak electrical signal and boosting it while maintaining the original waveform characteristics. There are several types: preamplifiers (prepare line-level signals), power amplifiers (deliver high current to speakers), and integrated amplifiers (combine both). Amplifier classes (A, AB, D, etc.) determine efficiency and sound quality – Class A offers pure analog reproduction but is inefficient, while Class D uses digital switching for compact size and high efficiency. Key specifications include power output (watts RMS), total harmonic distortion (THD), frequency response, and damping factor (control over speaker movement). Modern amplifiers may include features like Bluetooth connectivity, DSP processing, multi-zone support, and room correction technologies. High-end audiophile amplifiers use vacuum tubes for warm, harmonic-rich sound, while professional PA amplifiers prioritize reliability and power. Amplifier-speaker matching considers impedance (typically 4-8 ohms) and sensitivity (dB/W/m) to ensure optimal performance. Applications range from home theater systems and car audio to concert sound reinforcement and headphone amplification.