"on a loop" - that means that the recording plays over and over again. If you run a loop of recorded tape though a player, it never stops. The music (or whatever was recorded) never changes, either.
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Ann225I hate it whentheTV showsplaysrun in/on a loop all day.
Ann225The newshavehas beenplayingrunning in/on a loop all day; could you turn off the TV please?