Most likely originated around the time of Hanson's "Mmmbop"; an ear worm refers to any song that is so catchy, and at the same time extremely annoying, that it feels like a worm has crawled into your ear and eaten the intelligent parts of your brain so that you hum the song all day long, no matter how much you hate it.
-(Britney Spears' "Toxic" begins to play)
- Not that damn ear worm again!!!
Most recently used at Penn State University where it is used to describe a hardcore devouring of a substance (usually food); can also be used (less frequently) to describe how skilled one is at a particular task.