The term comes from "Wanted Words", a book (or set, actually, as there are two volumes) by Jane Farrow that grew out of her fascinating CBC show that no longer airs (for reasons passing understanding and most likely having to do with funding). It refers to a song that will not get out of your head no matter how hard you try. The apparent remedy is a brain-rinse, but that's only if you dislike the aneurythm more than the rinse, as the latter runs the risk of becoming the former.
Most are a nuisance.
Mine, however, is pretty okay for today. Michael Bublé is bouncing around in my head singing "Fever".
Katherine has been listening to Annie Haslam's (of the progressive rock band Renaissance) superior recording of Mike Oldfield's composition, "Moonlight Shadow" as well as Eimear Quinn singing "The Voice".
Strange mix, but it works….
Raising the Bar Strength & Conditioning 
Ah, good name for them. I’ve heard them called “earworms” as well. Whatever they are, I am VERY susceptible to them. Simple things seem to be catchier, too… I get silly simple things like “They Might Be Giants” songs on rotation for hours on end. Right now I’ve got a Hot Hot Heat song stuck in here… mindless catchy stuff. But anything I listen to often enough will go round and round and round.
You wanna know something really weird? The first time you get one of your *own* songs stuck in your head…
I’ll bet that’s truly a strange feeling. Surreal, in fact.