• Parkour has no set of rules, team work, formal hierarchy, or competitiveness.
• On the contrary it is more like an art or discipline that resembles self-defense in the ancient martial arts.
• According to David Belle, "the physical aspect of parkour is getting over all the obstacles in your path as you would in an emergency.   You want to move in such a way, with any movement, as to help you gain the most ground on someone or something, whether escaping from it or chasing toward it."Thus, when faced with a hostile confrontation with a person, one will be able to speak, fight, or flee.   As martial arts are a form of training for the fight, parkour is a form of training for the flight. 
• Practitioners move not only as fast as they can, but also in the most direct and efficient way possible, this characteristic distinguishes it from the similar practice of free running, which places more emphasis on freedom of movements, such as acrobatics.  
• Efficiency also involves avoiding injuries, short and long-term, part of why parkour's unofficial motto is être et durer (to be and to last).
• Traceurs claim that parkour also influences one's thought process by enhancing self-confidence and critical-thinking skills that allow one to overcome everyday physical and mental obstacles.
• A study by Neuropsychiatrie de l'Enfance et de l'Adolescence in France reflects that traceurs seek for more sensation and leadership than gymnastic practitioners.   They also have a more narcissistic personality, but one that does not seem to be linked to maladaptive or psychopathologic behaviors.

Source: Parkour - Wikipedia
Tips: How to Get Started in Parkour

An example of Parkour (taken from a film)

Le Parkour - Vancouver Film School(VFS)

Parkour Training

Parkour and FreeRunning

Jump Britain

Parkour Project:Pilgrimage