The spreading rate is a measure of how fast plate divergence is occurring. [Wikipedia]
The rate of recurrence of any periodic phenomenon, often associated with waves of all kinds. Without qualification frequency often means temporal frequency, the rate of recurrence of a time-varying function, but could mean spatial frequency, the rate of recurrence of a space-varying function. Spatial frequency is the reciprocal of the repeat distance (sometimes the wavelength). The dimensions of (temporal) frequency are inverse time. A common unit for frequency is cycle per second, formerly abbreviated cps, but superseded by hertz, abbreviated as Hz.
The frequency at which a displaced parcel will oscillate when displaced vertically within a statically stable environment.
The expansion or spreading out of a vector field; also, a precise measure thereof.