public address announcement; PA announcement in a venue
Refers to announcements made over a public address system inside a facility such as a stadium, station, airport, or event hall.
The train delay was announced over the station's PA system.
At the concert venue, a PA announcement is played before the show starts.
館内放送 is used for announcements inside a building such as a museum, library, or department store, while 場内放送 is more common for larger venues like stadiums, stations, or event halls.
Compound of 場内 (inside a venue) and 放送 (broadcast). The exact historical derivation is uncertain, but the word is a straightforward modern compound.