When you have a strong feeling that you have heard a familiar song before and you associate it with a time or an emotion, but you aren't exactly sure when or where you have heard the song. This usually occurs most strongly at the beginning of the song, but can last the entire duration as well.
When the otherwise seemingly happy song came on, Paul felt nostalgic and a bit depressed, although he wasn't sure why. He was experiencing musical deja vu.
I hate it when I get musical deja vu because I can't remember where I heard the song before.
when you are listening to your ipod or mp3 player to a song and you realize the same song is playing in the background at the same time (or very close to)
kid 1:dude i was just listening to eye of the tiger on my ipod at the gym and the same song came on in the background! i thought they only played shitty music at the gym
kid 2: holy shit you just had a musical dejavu
kid 1: jesus christ!!!!!