Circadian rhythm in biology refers to the internal physiological processes that follow a roughly 24-hour cycle, influencing behavioral and biological functions in organisms. This rhythm regulates sleep-wake cycles, hormone release, and metabolism, helping organisms synchronize with environmental changes such as daylight and temperature fluctuations. Disruptions to these rhythms can impact health, leading to issues like sleep disorders and increased susceptibility to diseases. Understanding circadian rhythms is crucial in fields like chronobiology and medicine.