Pool skating is an incredibly small division of skateboarding. Mainly because you need a pool. The pool must also be empty. Also, it must be of the west-coast, transitioned corner design. That is, there should be no sharp corners whatsoever between the sides and bottom of the pool, or between sides of the pool. Kidney-shaped pools tend to work well.
Pool skating was one of the original forms, along with freestyle and slalom. It was originated by the Z-boys in California. Their pool skating was based on carves and grinds on the coping. In fact, most well made bowls have coping that is similar to pool coping, for authenticity and feel during a grind. Pool skating was, in essence, the father of vert skating.
When skating a pool, most tricks done are inverts, grinds, carves, and slides. Sometimes, on bigger pools, you can get airs, but in most it is quite difficult. The main draw of pool skating is being able to skate more and more inhospitable pools. Carving over stairs, over pairs of lights, and airing over the deathbox.
Pool skating tends to be a guerrila activity, even when compared to street skating. Most pools are in abandoned houses in rundown, formerly upper-class neighborhoods. Steve Alba, a famous pool skater, has been rumored to fly over neighborhoods, scouting for pools. Once a pool is found, it must be dried up (most still have some water sitting, probably from rain or just left over) using sump pumps and kitty litter for finishing. Due to the amount of work put into prepping a pool, skaters tend to be quite territorial about their pools, and don't often spread word about the location of pools.
More recently, with the re-emergence of skateparks into cities, the bowl has become a legal alternative to pools. Some contests even have a bowl division.