where the tire is on the ground when you skid in relation to the pedals. For example, if I always skid with my right foot back and left foot forward (running 44x16) I will have 4 spot that will wear faster then the rest of the tire. If I can skid switch I will have 8 spots. The more skid patches, the more evenly your rear tire will wear while doing skids/skips.

damn you guys type fast! beat me to it.