polyphasic sleep
a pattern in which sleep occurs in relatively short naps throughout a 24-hour period. A human infant may begin life with a polyphasic sleep rhythm that consists of half a dozen sleep periods. The rhythm becomes monophasic, with one long, daily sleep period, by about school age. Biphasic sleep patterns, which include one daytime nap period in addition to the long, typically nocturnal, period of sleep, are seen in a variety of cultures (e.g., the siesta) and in older adults. Compare monophasic sleep. See also segmented sleep; sleep–wake cycle.