Six Degrees of Separation
is a concept tied to the Small World Experiment
of Stanley Milgram. The theory goes that all people are connected to all others through a fairly short pathway of common connecting people.
know someone 'a', who knows someone 'b', who knows someone 'c', who knows someone 'd', who knows someone 'e', who knows Person 'X'
. -- with person 'X; being anyone in the world
: President Obama, Kim Jong Il, or "the little old lady who lives at 4th and Broadmoor in Apt 37 in New York City". In theory, you could probably communicate a message with anyone in the world, regardless of their social status, if you only knew who it was to ask for help.
Milgram never initially used the term "Six Degrees of Separation", but it has been widely associated with the meme. The notion actually can be traced at least as far back as 1909 to early conjectures in communications theory, though Milgram's initial experiments took place in the late 60s. This has led to further understanding of the concepts of 'social networks', which is where ideas like Facebook and Twitter and such take strong powers from.