Here is what wikipedia says about it:
"Parkour is an art form of human movement, focusing on uninterrupted, efficient forward motion over, under, around and through obstacles (both man-made and natural) in one's environment. Such movement may come in the form of running, jumping, climbing and other more complex techniques. The goal of practicing parkour is to be able to adapt one's movement to any given scenario so that any obstacle can be overcome with the human body's abilities.
According to founder David Belle, the "spirit" of parkour is guided in part by the notions of "escape" and "reach"; that is, the idea of using physical agility and quick thinking to get out of difficult situations, and to be able to go anywhere that one desires. However, fluidity and beauty are also important considerations; for example, Sébastien Foucan, a traceur who trained with Andrew Hahn during the infancy of the art speaks of being "fluid like water," a frequently used metaphor for the smooth passage of barriers through the use of parkour. Similarly, experienced traceur Jerome Ben Aoues explains in the documentary Jump London that:
The most important element is the harmony between you and the obstacle; the movement has to be elegant... If you manage to pass over the fence elegantly—that's beautiful, rather than saying ‘I jumped the lot.' What's the point in that?
