1. repeating from the beginning
music/video played on a loop
A ‘loop’ is a circle, something playing ‘on a loop’ repeats from beginning to end and begins again. You might play music ‘on a loop’ in a store or if someone is repeating themselves often you can say it is as if they are ‘on a loop’. Similar in meaning to ‘repeating itself’ or ‘playing over and over’. This expression can be used in social and professional contexts.