Circadian rhythms refer to the 24-hour biological cycles that regulate the sleep-wake cycle, hormone production, body temperature, and other physiological processes in living organisms. These rhythms are driven by an internal clock located in the brain that helps synchronize the body's functions with the external environment, particularly the light-dark cycle. Research in circadian rhythms involves studying the mechanisms, regulation, and impacts of these biological cycles on various aspects of health and behavior. This field of research has important implications for understanding and treating sleep disorders, metabolic conditions, mood disorders, and other health issues.