It's a tie breaker that is used to rank people on the same overall score. So a person with 3/3 is ahead of those with 2/3, but those with 2/3 are sorted by their tie score.
It's calculated by looking at the rating of your opponents - the higher their rating, the higher your tie score is. Basically it's saying that 2/3 against stronger opponents is "worth" more than 2/3 against weaker opponents.
I do not understand what it is that "tie" in tournaments and especially how it is calculated?
thanks all