alsih2o said:more like-
an activity where a hypothetical individual, whose attributes and qualities are frequently expressed numerically, is acted by an inividual or group through scenarios usually designed to test creative possibilities and system restraints.
More seriously.
A character's attributes etc. need not be quantified at all. They could be expressed qualitatively, as in Eden Studio's Over the Edge. It is also possible that one could assume a role where only how a person will act in a situation is known, but not his abilities. While this falls more under the heading of "acting" than the traditional RPG, it still, in my opinion, falls under the definition I presented above.
Besides which (now that I've really read your version), not all sessions need include situations where creativity plays a part. Nor need the system be tested. Matter of fact, the last comes more under the aegis of meta-gaming, which is a matter for later discussion.