The Cut Off Point is a baseline point amount determined by the top players in a season. The first 100 games in a season are used to determine the top 100 players. The score set by the lowest ranked player of this group becomes the cut off point for the season. For the remaining games of the season, any points under that amount don't count.
EXAMPLE: Say the cut off point for a season of Team Death Match is 50. Steven and Layla are playing TDM; Steven scores 45 points, Layla scores 70 points.
Steven will recieve 0 points, as he did not reach the 50 point cut off.
Layla will receive 20 points (70 total minus the 50 point cut off.)
The idea of the cut off point system is to reward skillful play. You earn more points by killing higher ranked enemies, or by performing special kills (multi kills, grenade kills, etc) than you do hanging back and taking pot shots at easy targets.
NOTE: for the first 100 games you play, you will receive full points regardless of the cut off point for that season. The cut off point comes into effect for all games in a season beyond that.