Polyphasic Sleep

Polyphasic sleep is a term for going to sleep many times a day, rather than monophasic or biphasic, the two most common sleep schedules.  The idea behind polyphasic sleep is that one takes many small naps throughout the day, in effort to get more total waking hours in a 24-hour period.  The most extreme of these schedules is known as the "Uberman" sleep schedule, in which one takes a 20 minute nap, every 4 hours, which makes 2 hours of sleep per 24-hours (22 waking hours).  This schedule has problems, the largest being it is incredibly difficult to adjust to.  The first few weeks, one is in a state of sleep deprivation.  It takes incredible determination and discipline.  The naps need to be taken at exactly the same time (to the minute) each day for the schedule to work.  From the Uberman schedule, the "Everyman" schedule was developed, which is a "core nap" of 3 hours and 3 20 minute naps spaced throughout the day.  This schedule is a lot easier to adjust to and requires less discipline with the "micro naps".
Here is a chart from the Wikipedia page, visually comparing the different schedules:

Interestingly, Dymaxion sleep is the schedule used by Buckminster Fuller before the phenomenon of polyphasic sleep was ever described.  In fact, many figures through-out history utilized a similar sleep schedule, including: Leonardo da Vinci, Benjamin Franklin, Thomas Jefferson, Thomas Edison, Nikola Tesla and Winston Churchill.

Here are a couple more sites for information regarding polyphasic sleep:
Polyphasic Sleep: Facts and Myths

Polyphasicsleep.info