Definition: A measurement of the clubface's ability to rebound the ball, expressed as a percentage that is determined by a ball's speed off the clubhead divided by the speed at which it struck the clubhead.
The term came into the popular lexicon as ultra-thin-faced drivers began to proliferate. An effect of the thin faces is known as the "spring-like effect" or "trampoline effect": The face of the driver depresses as the ball is struck, then rebounds - providing a little extra oomph to the shot. A driver that exhibits this property will have a very high COR.
The maximum COR allowed under USGA rules is .830. Note: Not interchangeable with "spring-like effect." COR is a measurement; spring-like effect is what's being measured.
For a more in-depth discussion of coefficient of restitution, see the FAQ: What is COR?
Also Known As: COR, C.O.R.
