Six degrees of separation

Six degrees of separation is the idea that all people are six or fewer social connections away from each other. As a result, a chain of "friend of a friend" statements can be made to connect any two people in a maximum of six steps. It is also known as the six handshakes rule.^[1] Mathematically it means that a person shaking hands with 30 people, and then those 30 shaking hands with 30 other people, would after repeating this 6 times allow every person in a population as large as the United States to have shaken hands (7 times for the whole world).

The concept was originally set out in a 1929 short story by Frigyes Karinthy, in which a group of people play a game of trying to connect any person in the world to themselves by a chain of five others. It was popularized in John Guare's 1990 play Six Degrees of Separation.

The idea is sometimes generalized to the average social distance being logarithmic in the size of the population.