http://www.brainking.com/game/Help?ht=8

Here's what is says if you go there:
What does "S-B" column at tournament tables mean?
S-B is an abbreviation for Sonneborn-Berger system. It is used to specify an order of players with the same number of points and is based on a theory that points earned with a stronger opponent are more valuable than with a weaker one. The S-B value is a total sum of points of opponents who lost the tournament game with the player and half points of opponents who drawn the tournament game with the player. Only if two or more players have the same number of "normal" and S-B points, they share the same final order.