Smash Factor
Ball speed divided by clubhead speed, a launch monitor number that measures how efficiently you transferred energy into the ball.
A higher smash factor means more ball speed for the same swing speed, in other words, better contact. With a driver, 1.50 is a common target for a good strike (legal driver faces cap it around there under USGA/R&A rules); irons run lower, typically 1.30 to 1.40. A low number almost always points to a mis-hit away from the center of the face, not a swing-speed problem.
See the related guide: Launch monitor numbers explained
A full explanation, in plain language.
More contact & strike terms
Fat Shot (Chunk)
The club strikes the ground before the ball, losing speed and distance.
Thin Shot (Skulled)
Contact happens too high on the ball, sending it low and hot with no height.
Shank
The ball contacts the hosel instead of the clubface and shoots hard sideways.
Toe Strike
Contact made toward the far end of the clubface (away from the shaft) instead of the center.
Heel Strike
Contact made near the shaft end of the clubface instead of the center, a milder cousin of a shank.
Sweet Spot
The small area on the clubface (roughly the center) that produces the most efficient, powerful contact.