Mountain Biking

Mountain biking is a sport which consists of riding bicycles off-road, often over rough terrain, using specially adapted mountain bikes. Mountain bikes share similarities with other bikes, but incorporate features designed to enhance durability and performance in rough terrain. Mountain biking can generally be broken down into multiple categories: cross country, trail riding, all mountain, downhill, freeride, street riding, dirt jumping and trials. The vast majority of mountain biking falls into the recreational XC and Trail Riding category.

Downhill Biking (DH)
Downhill biking (DH) is a gravity-assisted time trial mountain biking event. Riders race against the clock, usually starting at intervals of 30 seconds (seeded from slowest to fastest), on courses which typically take two to five minutes to complete. Riders come from all around the world. Riders are timed with equipment similar to that used in Downhill skiing. The placing is determined by the fastest times to complete the course; races are often won by margins of under a second. As the name of this discipline implies, downhill races are held on steep, downhill terrain, resulting in high speed descents, and with extended air time off jumps and other obstacles.
Source: Wikipedia