Six Degrees of Kevin Bacon
This is a game, whose title is a Mondegreen of Six Degrees of Separation, in which it is said that any actor can be linked through his or her film roles to actor Kevin Bacon within six steps. For example, George Clooney was in Ocean's Eleven with Matt Damon, Matt Damon was in The Departed with Jack Nicholson, and Jack Nicholson was in A Few Good Men with Kevin Bacon. It should be noted that this spreads across all actors; Megumi Hayashibara can be linked to Kevin in only two moves. It's often a game for film nerds to test the abilities of each other.
There is a whole website dedicated to this found here.
Mathematicians have extrapolated this phenomenon and given it a name: "Bacon Number", which sounds like one of those impossibly high numbers with dangerous implications for the future of the universe but is in fact incredibly low. Researchers have demonstrated (true story!) that almost everyone has a Bacon Number < 10, due to Kevin Bacon appearing in, mathematically speaking, almost every film on the planet. For instance, Kevin Bacon himself has a Bacon Number of 0. Chew on that, Mr. T!
Curiously, the most connected person in acting is not Kevin Bacon. Research by people who found it important enough to do so discovered that the centre of the Hollywood universe shifts over time, and has rested with Dennis Hopper, Harvey Keitel, Donald Sutherland, Rod Steiger, and Eric Roberts at one time or another.
Mathematicians (and all scientists) also have a similar ranking called the Erdos Number, based on co-authorship of mathematical articles with deceased mathematician Paul Erdos. Inevitably there's a combination, the Erdos-Bacon number, based on adding the two together. Thanks to the documentaries, and occasional extra work on math-related films, some mathematicians have Erdos-Bacon numbers as low as 3. More surprising are actors who attack the problem from the other side. Danica McKellar (Winnie from The Wonder Years and bona-fide mathematician) and Natalie Portman (wrote a psychology paper at Harvard with an Erdos link) each have Erdos-Bacon numbers of 6. (This ties them with Richard Feynman.)
For applications in fiction, see One Degree of Separation.
To find an actor's Bacon Number, consult The Oracle of Bacon.
No relation to Bacon Addiction.