Parkour is defined as the efficient movement towards a certain point to another in the case of an emergency, such as a chase or reach scenario. The movements utilized include sprinting, running, vaulting, jumping, climbing, quadrupedal movement, rolling, etc. All natural human movements can be considered as Parkour as long as these are efficient, thus decreasing energy expenditure, time, distance, or danger to the practitioner or traceur.
some brittish guys saw it in spiderman and were all like oh shi I can do that shit easy brav init. and learned to climb walls, the reast is history.
Physicality of the discipline
Due to the nature of the discipline, it can be considered as very stressful for the traceur's body, for this reason complimnetary strengtheining and condition is recommended by some. However, the parkour community seems to be divided when it comes to this subject. Most of the practitioners opt for only parkour and techniques as a means to strengthen the body, and while this method does work to a certain point, it is certainly obsolete at increasing the total amount of strength and power in a prolonged amount of time. There is also a big controversy as to include weight lifting as training regiment for parkour, but over time it seems to be gaining momentum in some communities and amongst some practitioners, which is a big step from the all bodyweight regimes followed by most practitioner, which again is not bad, but then again there are more "efficient" ways to obtain strength and other skills.
Parkour differs from a sport only because it has a philosophical aspect to it. Parkour was originally created as a means to help others, to be useful to others as well as for oneself. However if this was the case, most traceurs would train differently. Rather than doing a jump countless times, they could develop more overall physical preparation, in order to use it in any given situation that is needed. Also the concept of being useful to your fellow should not disappear as soon as training is over, it should be something that the traceur should does in his daily life. Practitioners also say that parkour helps overcome life's problems by making you confront obstacles in your personal or daily life, just like you would outside while training.