The definition of an earworm is a bit of music that stays in your head.
An example of an earworm is a catchy advertising jingle.
A melody or a portion of a piece of music that is involuntarily repeated in one's mind.
A tune that is stuck in one's head, especially as unwanted or repetitive.
Origin of earworm
Sense 2, translation of German Ohrwurm earwig, (musical) earworm Ohr ear Wurm worm