The difference between overdrive and distortion on guitar?

A friend of mine was trying to explain it to me, but I didn't quite understand. For instance, would the beginning of this song (a href="http://www.youtube.com/watch?v=Vsapab5LwcY)" rel="nofollow"http://www.youtube.com/watch?v=Vsapab5Lw…/a be considered distorted guitar or overdrive...?