Play piercing is piercing, ususually using hypodermic needles, "for the pure fun of it." Jewelry is rarely inserted, as the point of play piercing is simply to experience the sensations of being pierced. Often, ribbons are laced between the needles to give a 'corset' effect.
The reasons for engaging in this sort of play are extremely diverse. Some people do it for enlightenment, while others do it for purely sexual reasons (play piercing got started in the BDSM subculture) either on their body or genitally in acts such as CBT. Others use it as a precursor for or pulling, and almost all will agree that it has mind-expanding effects.