Biphasic and polyphasic sleep

Biphasic sleep means that you sleep twice in a 24-hour day. During the day, most people sleep once for 7-8 hours. But people who use biphasic sleep sleep twice - once during the day, and then again at night for about 4-5 hours.

Polyphasic sleep means that you sleep more than twice in a 24-hour day. People who use polyphasic sleep usually take 3-4 short naps throughout the day. These naps typically last 1-2 hours and add up to around 4-6 hours of total sleep time.