There are two types of sleep: Monophasic and Polyphasic. By about 7 years old most people in the United States practice Monophasic sleep, or sleeping for one solid chunk of time from 6 to 9 hours, usually at night.
Interestingly, we are all born practicing Polyphasic sleep – rotating through a cycle of sleep and awake time through-out the day. Most babies are trained into sleep cycle where they sleep 8+ hours a night, with a nap or two during the day by about 1 year of age, and beteen by 5 and 7 most of them have given up the nap and are now completely monophasic.
At least this is true in the United States. Mexico is famous for its siesta, but it is actually practiced in many other parts of the world. Also, a large portion of Europe used to nap during the day, and then have some awake time at night. They are moving away from this in an effort to more align themselves with the US I imagine.
To sum it up, we are born polyphasic sleepers, which is breaking sleep up over multiple “naps” during a single day, but at least in the US we force ourselves to become monophasic, which is to sleep in one solid chunk once a day.
There is not many types of monophasic sleep. Some sleep less, other sleep more. Some sleep at day, others at night. That is about it.
Polyphasic sleep on the other hand is very varried. The most famous, and probably the most difficult type is called Uberman where there are 6 naps from 15 – 30 minutes throughout the day, and that is it. At the other end of the spectrum is a shorter sleep block at night, with a nap during the day.
My wonderful wife Dawn actually adopted a modified polyphasic sleep schedule to help our son deal with some behaviorial labels the school was placing on him. The two of them go to bed and get up at a normal time, but they are up for 15 – 30 minutes in the middle of the night, and then take a 15 – 30 minute nap during the day. By breaking up the sleep like this causes a calming effect. She has written about it in her blog. (Using polyphasic sleep to deal with Aspberger’s syndrome and Polyphasic sleep update).