A public address or "PA" system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a given sound, e.g., a person making a speech, prerecorded music, or message, and distributing the sound to the general public around a building.

Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with a larger number of speakers are widely used in institutional and commercial buildings, to read announcements or declare states of emergency. Intercom systems, which are often used in schools, also have microphones in each room so that the occupants can reply to the central office.

The PA Systems are also called as Sound Reinforcement (SR) systems. Some audio engineers distinguish between the two by technology and capability, while others distinguish by intended use, e.g., SR systems are for live music, whereas PA systems are usually for reproduction of speech and recorded music in buildings and institutions). This distinction is important in some regions or markets, whileq1 in other regions or markets the terms are interchangeable.