Compression (Ball)
A rating (roughly 30 to 100+) of how much a golf ball deforms on impact, which affects feel more than distance for most golfers.
Despite the common myth, compression isn't really about your swing speed, it's a fixed property of the ball itself. A softer, low-compression ball feels softer off the club and is often easier to compress fully even at slower swing speeds, but the actual distance difference is smaller than most golfers assume. This is a different idea from "compressing the ball" as a swing feel (hitting down and through with forward shaft lean), which is about technique, not the ball's spec.
See the related guide: Golf ball compression, explained
A full explanation, in plain language.
More equipment terms
Loft
The angle of the clubface relative to a vertical plane, which controls launch angle and, largely, distance.
Lie Angle
The angle between the shaft and the ground when the club is soled correctly at address.
Bounce
The angle built into the sole of a wedge that helps it glide through sand or turf instead of digging in.
Offset
A design feature where the leading edge of the clubhead sits slightly behind the hosel.
Shaft Flex
How much a shaft bends during the swing, rated from Extra Stiff down to Ladies/Senior flex.
Cavity Back vs. Blade
Two iron head designs: cavity-back irons hollow out the back of the head for forgiveness, while blades (muscle backs) are more compact for feel and control.