Road running is the sport of running on a measured course over an established road. This differs from track and field on a regular track and cross country running over natural terrain. These events are usually classified as long-distance according to athletics terminology, with races typically ranging from 5 kilometers to 42.2 kilometers in the marathon. They may involve large numbers of runners or wheelchair entrants. The four most common IAAF recognized distances for road running events are 5K runs, 10K runs, half marathons and marathons.