A<unk>  is an approximate daily periodicity, a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living beings, including plants, animals, fungi and cyanobacteria. The term<unk> ", coined by Franz Halberg, comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day." The formal study of biological temporal<unk> s such as daily, tidal, weekly, seasonal, and annual<unk> s, is called chronobiology.
In a strict sense,<unk> s are endogenously generated, although they can be modulated by external cues, primarily daylight. They allow organisms to anticipate and prepare for precise and regular environmental changes.
Circadian rhythm
Menstrual cycle
Diurnality
Human physiology
Sexual maturity
Hemodynamic response
Vagovagal reflex
Renal physiology