P90X is a workout designed to avoid "plateaus" in your workout gains. It works by something called "Muscle Confusion", and incorporates lots of different exercises in the routine. You also add new routines and movements during the time you're on the program. Essentially, it attempts to exercise the muscles in different ways so they don't get used to one particular routine or movement. Apparently, all you really need is a resistance band to do it effectively.
