The frequency and wavelength of vibration from the cue hitting the ball off center is the result of nodal points (stationary points).

Webster's says, "A point in a vibrating system that is constantly free or relatively free from vibratory motion."

Also--in a vibrating media (pool stick), that point which remains at rest while the other parts of the body are in a state of vibration.

Nodal points are a barometer of how a cue is flexing. The flex is affected by weight distribution, stiffness, shape, how tight or loose you grip the cue, as well as, where you grab the cue (in the middle of the wrap or near the butt).

Basically, the further back you grip a cue (for example: a tall person) the stiffer the action you receive from the cue.