Brace hieght is the distance from the string to the deepest part of the grip. The higher the brace height, the more forgiving it is, the lower the bace height, the faster the bow will be. If the brace height is high, the arrow is on the string longer, which means more of a chance of you messing up the shot after you hit the trigger, but it will slow the arrow down though, since the power stroke is shorter.