A circadian rhythm, popularly referred to as body clock, is an endogenously driven (non-reliant on environmental cues), roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria (see bacterial circadian rhythms

Bacterial circadian rhythms

Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three characteristics: in constant conditions Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three...

). The term circadian comes from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 circa

Circa

Circa , usually abbreviated c. or ca. , means "approximately" in the English language, usually referring to a date...

, meaning "around", and diem or dies, meaning "day".