The act of copying a certain contacts song over MSN, (or any other instant messaging service where their music is shown), and basically listening to whatever they listen to.
Used for finding new music, an insight to the contacts music tastes or just to creep the other person out, providing they're smart enough to realise.
Girl) Dude! wtf are you song stalking me? you've been listening to whatever im listening to for the past hour!
Guy) Shut up hoe