The venue auditorium sound system. Usually shortened to "PA".

A paging system whereby a person can be heard in remote areas of a building for the purpose of making announcements. Different from a sound reinforcement system which helps reinforce the already existing sound (the sound people already can hear, but isn't loud enough).

a useful option, to enable announcement of stop names and destinations, and to give other information to passengers, especially those who are blind or partially sighted or in need of special help

an electronic amplification system used as a communication system in public areas