A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to speak to a large public, for example for announcements of movements at large and noisy air and rail terminals or at a sports stadium or amplify other audio content, such as recorded music or the live sound of a band.

Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations, such as schools, stadiums and large passenger vessels and aircraft. Intercom systems, installed in many buildings, have both speakers throughout a building, and microphones in many rooms allowing the occupants to respond to announcements.