(courtesy University of Science and Philosophy)
Periodicity in time is often specified by its frequency, the inverse of the repetition period, which has the metric units of hertz (the number of periods per second).
Oscillations, waves and standing waves have crests at periodic intervals of space and/or time .(Wikipedia)
noun: the quality of recurring at intervals. Repeating, cyclical.
Law of Assimilation
Rhythmic Balanced Interchange
Universal Heart Beat