Polyphasic sleep refers to any pattern where your sleep is taken in more than one chunk. Spanish siestas are an example of this, and Spain has the only culture I know of that is not generally monophasic. Other, more unusual polyphasic patterns are those involving multiple naps per day, and sometimes no large chunk of sleep at all.
I became interested in polyphasic sleep some years back but only recently did I realize that here at Instructables, I had an organization that might allow me to experiment with different sleep patterns. Instructables is ALL ABOUT weird shit like this. So I and my boyfriend are making the attempt.
The pattern we are using is to nap for 20 to 30 minutes every four hours, throughout the day. (This is sometimes referred to as the Uberman pattern, although personally I dislike this term.) This comes out to about 2 - 3 hours of sleep per day, broken up into bits. The theory behind it is that after a week or so of sleep deprivation and general bleariness, your body adjusts to the short but regular naps and goes directly into REM sleep. Thus after a while you are getting enough sleep and feel fully rested - but you have an extra 5 or 6 hours every day to do Stuff in.
In this Instructable I'll document my experiences with polyphasic sleep. I'll write one step a day for a while, and once I settle into the pattern - if I settle into the pattern - I will add a step occasionally as something interesting occurs to me.
Google Search in case you want more Internet-style information.