piRates (hee hee, that's what I call it too)=body conditioning, promotes physical harmony and balance. Its about strength, posture and core stability. The "powerhouse" - abdomen, lower back, and buttocks - is supported and strengthened, enabling the rest of the body to move freely.
Sort of like yoga, but much more focused on making sure you're using the right muscles to do things. It builds strength and flexibility without bulk.
I'm using it mainly to sort out: proper breathing, developing the muscles to let me hold my pelvis still (=less wiggly paddling), strong internal abs to support my spine and prevent overuse of lower back and to get more flexibility and strength around my thoracic vertebrae (where my scoliosis is).
I do yoga and weights as well. I only do about an hour of piRates a week, I never get bored in piRates, sometimes I get bored in yoga and when I'm swimming.
Have a google, lots of stuff on the interweb.