A song that sticks in your mind, and will not leave no matter how much you try.
The best way to get rid of an earworm is to replace it with another. Be prepared to become a jukebox.
worst examples: "Mmmbop" by Hanson, "Toxic" by Britney Spears
, "Quit Playin Games With My Heart" by Backstreet Boys, or any damn Hilary Duff
best examples: "This Love" Maroon 5, "Hey Ya" Outkast, "Memory" Sugarcult, and any Lauryn Hill