Vertical direction the clubhead is moving at impact. Downward strike is negative; upward strike is positive.

Highest point of the ball’s flight.

Spin that influences total lift (see lift). Too much can balloon and waste speed; too little reduces carry.

Speed of the ball immediately after impact. Primary contributor to distance and lift (see lift).

Is the club designed with a bias, either draw or fade?
When everything is neutralised and the head is delivered to the golf ball with a 0 club path, 0 face-to-path, neutral dynamic lie, and a zero-zero perfect strike, will the golf ball still fly with a bias to its trajectory?
Different golfers will want different things, so knowing a club’s bias to curve the golf ball is key.

Distance traveled through the air before first ground contact.

Speed of the clubhead at impact.

Horizontal direction the clubhead is traveling at impact relative to the target line (in-to-out or out-to-in).

How quickly the clubface is rotating (opening/closing) through impact. Higher values typically increase timing sensitivity.

Angle the ball is traveling downward at landing. Higher descent generally stops faster.

The spread of shot results (left/right and short/long). Used to judge consistency, not just best-case distance.

Vertical Spin Change is, per mm of vertical miss, how much more or less spin changes as a % of middle-strike spin.
Strike moving vertically on the club face will produce different ball flights. High on the face will gear the golf ball to lower spin, and low on the face will gear additional spin.
As a general rule of thumb, a more stable spin profile on a driver is preferred for consistent trajectories.

Spin Axis Change is, per mm of horizontal miss, how much tilt-axis spin changes in degrees per mm of miss.
Strike moving laterally on the club face will produce different ball flights. A heel miss will gear the golf ball to fade spin, and a toe miss will gear draw spin.
As a general rule of thumb, a more stable spin profile on a driver is preferred for consistent trajectories.

Loft actually presented at impact after shaft lean, handle position, and face orientation are accounted for.

Where the face is pointed at impact relative to the target line (open/closed). Strong driver of start direction.

Face angle relative to club path. A major driver of curvature.

A loft-normalized efficiency concept: By removing loft from the smash factor we can compare how fast a club head is against any other for any golf delivery.

Our term for the spin produced by a specific club, its loft adjusted and swing speed adjust so regardless of delivery two clubs can be compared.

Shot that curves left-to-right for a right-handed player (opposite for left-handed).

A measure of how well a club retains ball speed (and therefore distance) when not hitting the center of the face.

Curvature/spin changes caused by off-center strikes twisting the head during impact (most relevant for drivers/woods).

Time from launch to landing.

Where the ball contacted the face, usually described toe/heel (horizontal) and high/low (vertical). Strongly affects speed, spin, and direction.

Initial vertical angle of the ball’s flight immediately after impact.

How effectively delivered loft becomes launch. Helps describe whether a club/strike launches “high for its loft” or “low for its loft.”

Aerodynamic force that keeps the ball in the air. A spinning ball produces lift based on forward speed and spin.

A general normalization concept: adjusting an efficiency metric so shots with different delivered lofts can be compared on a common loft reference.

Lowest point of the swing arc relative to the ground. Strongly influences contact, AoA, and turf interaction.

Resistance to twisting. Higher MOI generally reduces twisting on off-center hits, often tightening dispersion and reducing speed loss.

Sideways miss distance relative to the target line (often measured at landing).

Maximum height reached during flight.

Start-direction terms. Push starts right of target (RH player); pull starts left. They describe start line, not curvature.

Distance traveled on the ground after landing.

Combined description of start direction and curvature (e.g., “starts right, fades back”).

Is the metric for how well the club transfer energy to the ball, when all other things are equal the higher the smash factor the better. It ranges in values from 1.48 on Driver to 1.2 on a PW.
The highest smash factor a club can achieve is limited by three things.
1.    The weight of the head of the club, the heavier the head the higher the possible smash. +10g of head weight, increases max smash ~0.01
2.    The PGA limit of any club being 83% efficient in the spring effect of the face.
3.    The delivered loft of the club, the lower the loft the closer the maximum limit. 4 degrees difference I delivered loft changes smash by ~0.05.

The tilt of the spin direction that determines curvature. More tilt generally means more curve. It results from the face angle and club path not matching (see face-to-path).

A delivery term describing the relationship between delivered loft and angle of attack. The driving force for left-to-right accuracy; higher spin loft is why the short irons (9–PW) are easier to hit straight vs the long irons (4–5) or even driver.

Initial direction the ball launches relative to the target line.

Carry plus rollout.

Overall spin rate magnitude (rpm). Does not describe curvature by itself without spin axis.