Rhythm (from Greek ῥυθμός, rhythmos, "any regular recurring motion, symmetry" ()) generally means a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions" (, 2537). This general meaning of regular recurrence or pattern in time can apply to a wide variety of cyclical natural phenomena having a periodicity or frequency of anything from microseconds to several minutes or hours, or, at the most extreme, even over many years.