Infradian rhythms are biological rhythms that occur over a period longer than 24 hours. These rhythmic cycles govern various physiological and behavioral processes in living organisms.

Infradian rhythms are classified as one of the two main types of biological rhythms, the other being ultradian rhythms. Unlike ultradian rhythms, which have a period shorter than 24 hours, infradian rhythms have a longer duration and typically exhibit cyclical patterns over days, weeks, months, or even years.