An earworm, sometimes referred to as a brainworm, sticky music, stuck song syndrome, or, most commonly after earworms, Involuntary Musical Imagery (INMI), is a catchy and/or memorable piece of music or saying that continuously occupies a person's mind even after it is no longer being played or spoken about. Involuntary musical imagery as a label is not solely restricted to earworms; musical hallucinations also fall into this category, although they are not the same thing. Earworms are considered to be a common type of involuntary cognition. Some of the phrases often used to describe earworms include "musical imagery repetition" and "involuntary musical imagery".

The word earworm is a calque from the German Ohrwurm. The earliest known English usage is in Desmond Bagley's 1978 novel Flyaway, where the author points out the German origin of his coinage.

Researchers who have studied and written about the phenomenon include Theodor Reik, Sean Bennett, Oliver Sacks, Daniel Levitin, James Kellaris, Philip Beaman, Vicky Williamson, Diana Deutsch, and, in a more theoretical perspective, Peter Szendy, along with many more. The phenomenon should not be confused with palinacousis, a rare medical condition caused by damage to the temporal lobe of the brain that results in auditory hallucinations.