Biorhythms refer to the internal biological cycles that repeat over a specific period. Alternative words for biorhythms include chronobiology, circadian rhythm, biological clock, and body clock. Chronobiology is the study of the physiological and behavioral responses of living organisms to cyclical changes in their environment. Circadian rhythm is the natural, internal process that regulates the sleep-wake cycle and other physiological processes over a 24-hour period. Biological clock is a term used to describe the internal timing mechanism that regulates various biological processes. Body clock is another synonym for biorhythms that refers to the innate, natural timing mechanism that regulates various physiological functions in living organisms.