Balance point - The point at which a shaft achieves equilibrium; the point where a shaft has weight evenly distributed on both sides of a given point.

Bend point - The point of maximum bending on a shaft as measured by compressing both ends inward.

Centrifugal force - Latin origins (centrum "centre" and fugere "to flee"). Forces acting away from the centre of rotation when an object is rotated.

Coefficient of restitution - Abbreviation is COR. The ratio of the relative speeds of the colliding bodies after impact to that before impact and as such can take a value between zero (perfectly plastic collision where all energy is lost in the collision) and one (perfectly elastic collision where all energy is transferred from one object to the other). 

Deflection - The deviation of the tip from the butt centreline after a known unit of force is applied to the tip to create a curve in the shaft.

Flex - The designation assigned to a shaft based on its stiffness or ability to resist bending - ladies (L), regular (R), stiff (S) and extra stiff (X).

Frequency - The number of oscillations of a shaft over a known period of time after the tip is pulled down and released while mounted in  a frequency-measuring. Units of measurement are cycles per minute (CPM). 

Kick point - The point of maximum bending on a shaft as measured by deflecting the tip end of the shaft only.

Moment of inertia - Abbreviation is MOI. The reluctance of an object to rotate about a given axis. Units of measurement are kg.mm².

Smash factor - the ratio of ball speed to clubhead speed. The theoretically "perfect" smash factor for a conforming driver is 1.5.

Spine - A longitudinal line or plane on a golf shaft that is more resistant to bending than any other line or plane.

Swingweight - The measurement of a golf club's weight distribution about a fulcrum point which is established as a specific distance from the grip end of the club.

Torque - The resistance of a shaft to twisting. Units of measurement are degrees.

Bibliography

Butler, H & Winfield, D. (1995). What shaft is best for you? In Golf: The Scientific Way (edited by A.J. Cochran), pp. 113-115. Hertfordshire: Aston Publishing.

Hocknell, A. (2002). High-performance driver design: benefits for all golfers. Journal of Sports Sciences, 20, 643-649. 

Horwood, G. (1995). Flexes, bend points and torques. In Golf: The Scientific Way (edited by A.J. Cochran), pp. 103-108. Hertfordshire: Aston Publishing. 

Maltby, R. (1995). Golf Club Design, Fitting, Alteration & Repair: The Principles & Procedures (4th Edition). Newark, OH: Maltby Enterprises.  

Summitt, J. (2000). The Modern Guide to Shaft Fitting. Newark, OH: Dynacraft Golf Products, Inc.

Wishon, T.W. (1995). Modern shaft fitting - combining flex and torque. In Golf: The Scientific Way (edited by A.J. Cochran), pp. 119-121. Hertfordshire: Aston Publishing.