Dexterity defines ones fine motor, flexibility, reaction speed, and general lithe.

Dexterity is applied to your AC, and also increases damage dealt for weapons that have Dexterity-scaling. Dexterity is quite important for someone agile, involved in much combat, or trying to perform meticulous tasks like lockpicking very often. Not only does it measure how adept you are at dodging attacks in combat, it can help you save your neck in a split second reaction, or get a stable landing from a jump off a ledge. Even ones movement speed in combat scaled with their Dexterity.