Cryptokitties leaderboards

Collection - shows how far you from the full set collection;
Num low score - shows your score where low number is the best factor;
Num high score - shows your score where high number is the best factor;
Gen low score - shows your score where low generation is the best factor;
Gen high score - shows your score where high generation is the best factor;
The difference (score) is taken between each score and the best possible score, making 0 always a perfect score.