It's an innate periodic cycle in an organism's physiological processes as in sleep & wake cycles
Some rhythmic processes are more affected by the circadian clock than by the 
sleep-wake... [DOC] [TLE] Circadian Rhythms, Biological Clock, Chronobiology - Crystalinks [PAR] A circadian rhythm is any biological process that displays an endogenous, 
entrainable ... Circadian rhythms can influence sleep-wake cycles, hormone 
release, body ...