The rhythm is the biological rhythm that occurs over approximately 24 hours.

The circadian rhythm is the biological rhythm that occurs over approximately 24 hours.The rhythms is defined with physical, mental and behavioral changes that follow a roughly 24-hour cycle. This rhythm is our body clock, that regulates the timing of periods of sleepiness and wakefulness throughout the day.
This 24-hour rhythm is driven by a circadian clock, and it has been widely observed in plants, animals, and  fungi.