-A "P trap" has its waste pipe going out through the wall at the back.
-An "S trap" has its waste pipe going down through the floor. This is more common.
The importance here is that an "S trap" toilet will not go into "P trap" plumbing and vice versa. So what you may see in a catalogue may not work with your existing plumbing. We have a wide range in store and on catalogue that can help you get what's will work for you.