Swing speed is a measure of velocity, in miles per hour, of how fast the club head of a golf club is traveling at the point it makes impact with the golf ball. Swing speed can be recorded by a launch monitor or other electronic radar devices.
any swing speed
Shown in miles per hour
Balls designed for higher handicap golfers generally have harder covers that result in lower spin rates with irons and drivers. Balls designed for low handicap golfers tend to offer your more control and spin.
20 or higher
Shown in strokes
Trajectory is a term used to describe the flight characteristics of a golf shot. It considers the height of the shot as well as it's launch and landing characteristics.
Feel is a term that considers the firmness or compression of the golf ball. Typically the softer the golf ball feels, the lower the compression rating. A general rule of thumb about golf ball compression is that players with a lower swing speed should use a lower compression ball to take advantage of the added spring affect.
9 iron spin is regarding the backward rotation of the golf ball in flight or the measured rate of that rotation. Most golfers think of backspin more in relation to shorter irons and wedges. Backspin is what causes some wedge shots to "back up" on the green, or roll backwards after hitting the green.