The term diurnal refers to activities or patterns that occur during the daytime or within a 24-hour period. It is often used in biology to describe animals or plants that are active during the day and inactive at night as opposed to nocturnal animals who are active at night. In meteorology, diurnal variations refer to the changes in temperature, humidity, and wind that occur during a 24-hour cycle. Additionally, diurnal rhythms refer to natural patterns of behavior or physiological processes that recur on a 24-hour basis, such as sleep-wake cycles and human circadian rhythms.