Parkour sometimes abbreviated to PK means l'art du déplacement which in English means the art of movement. Parkour is an activity with the aim of moving from one point to another as smoothly, efficiently, and quickly as possible, using principally the abilities of the human body. It is meant to help one overcome obstacles, which can be anything in the surrounding environment—from branches and rocks to rails and concrete walls—and can be practiced in both rural and urban areas. Injuries, sometimes permanent, from jumping, twisting and falling are common. Parkour practitioners are referred to as traceurs, or traceuses for females.
Parkour was developed by the French army, soldiers had to learn the technique to escape dangerous areas or when they had been captured; to escape. Later it became popular among the normal people and it had been trained to move around in urban areas at high speed or just for fun.
In truth there is no difference between Free-Running and Parkour except for the fact that most people who call themselves Freerunners (someone who does Free-Running) learn tricking moves while people who call themselves Traceurs (someone who does parkour) do not. Tricking itself is a completely different disipline.