Parkour is a discipline not unlike martial arts, but rather than practicing fighting or self defense, it is about moving efficiently
Parkour is a way of moving from one place to another as quickly and as efficiently as possible by means of jumping, vaulting, climbing and other such things.
Parkour is not to be confused with freerunning
, which is more focused on aesthetics (i.e. flips, aerials etc.) rather than efficiency. Freerunning is considered an extreme sport, wheres Parkour is a practice for personal benefit rather than showing off.
One who practices Parkour is known as a traceur
I saw this guy using Parkour to get to wherever he was going. I saw him climbing walls, vaulting shorter walls and jumping to get wherever he needed to be as quickly and as efficiently as possible.