The axis of rotation of the wheel.

the tilt of the backspin direction (tilted to the right causes a curve to the right, and vice versa) Example: The more tilted the spin axis the more the ball will curve.

Spin Axis is the axis that the ball spins on or the measure of the tilt of that axis. A positive Spin Axis means that it is tilted to the right (a slice or face for RH golfers). A negative Spin Axis means that is it tilted to the left (a draw or hook). It is often compared to the wings of an airplane. If the plane’s wings tilt to the left, the plan [..]

As the ball spins around an axis, the measure of axial tilt. Positive means the axis is tilted to the right (thus resulting in a fade or slice for a right handed golfer), negative means the axis is ti [..]

Spin axis is the measure of tilt of the axis around which the golf ball spins.

An open or closed clubface will cause the spin axis to tilt putting curvature on the ball during flight.