It's the postulation that links anyone with any other person, alive or dead, by means of intrinsic association:
Me... 1. My NYU animation teacher (dialogue syncher for "Beavis and Butt-head") 2. Mike Judge (creator of "Beavis and Butt-head")
Mike Judge (director of "Beavis and Butt-head Do America")... 1. Bruce Willis (voiced a character in "Beavis and Butt-head Do America") 2. Halle Berry (co-starred with Willis in "Perfect Stranger") 3. Pierce Brosnan (co-starred with Berry in "007: Die Another Day") 4. Denise Richards (co-starred with Brosnan in "007: The World is Not Enough") 5. Kevin Bacon (co-starred with Richards in "Wild Things")
... thus the name of the game being "Six Degrees of Kevin Bacon" - the goal being to use the least associations to link anyone to Bacon, since he allegedly starred in every movie ever made. The man is busy.