BOUNCE The degree to which the sole of a club angles up and away from the ground plane when the club is in a square setup position. In general, more bounce is better for soft sand and high, lush grass; less bounce is better for firm sand and turf.
BULGE The face curvature from heel to toe that corrects spin on mis-hits.
CAMBER The radius measurement of the sole from front to back or heel to toe.
CENTER OF GRAVITY (CG) A theoretical point that defines the average location of weight in a clubhead and the internal point about which an object rotates. A low CG helps to launch the ball higher. A club's CG isn't always found at its geometric center.
CHAMFER A beveled or rounded edge connecting two surfaces.
COEFFICIENT OF RESTITUTION (COR) Used by manufacturers to refer to the springlike effect of a flexing clubface. The U.S. Golf Association limit is .83, which refers to the efficiency of energy transfer between two colliding bodies (clubhead and ball). The way a thin-titanium clubface flexes can reduce the way the ball deforms at impact, therefore decreasing the loss of energy transferred to the ball.
LEADING EDGE The forward edge of the sole, opposite the trailing edge.
MOMENT OF INERTIA (MOI) The measure of a club's resistance to twisting on off-center hits (sometimes called forgiveness). The USGA limit for drivers is 5,900 grams/centimeters squared. Golf Digest, with help from David Lee, associate professor at Gordon College, tested the MOI ratings for each driver that made our Hot List, using one sample head from each club. We then sorted the drivers into three groups. Drivers labeled "HIGH" had an MOI test number from 4,000 to 4,600. Drivers labeled "VERY HIGH" had a test number from 4,700 to 5,300. Drivers labeled "EXTREME" had a test number higher than 5,500. The Nike Sumo2 5900 had the highest MOI number of any driver we tested.
RELIEF The angling or curve up and back of the sole to reduce turf contact.
SKIRT The perimeter of a clubhead between the sole and crown.