Public address (PA) systems are used to amplify sound so that more people can hear it. They are used in public venues where an announcer or performer needs to be heard over a large area. For example, PA systems are used for announcements at noisy airports and train stations. They can also be used for playing background music or speaking to a large crowd hospital, Industrial like..
PA systems are made up of a microphone, amplifier, and loudspeakers. They can be used indoors or outdoors, and can be installed as ceiling, wall, or outdoor speaker systems
The most basic example of a PA system is a megaphone, which is a single microphone and speaker.