Cycling sport is an activity that involves riding bicycles for sport, recreation, or transportation. Synonyms for cycling sport include bike racing, road cycling, mountain biking, bicycle motocross (BMX), cyclocross, and track cycling. Bike racing entails competitive events that happen on roads, tracks, and off-road courses. Mountain biking is a specialized form of cycling sport that involves riding bikes on rough terrain, such as steep slopes and uneven surfaces. BMX involves riding bikes in a closed looped course, often featuring jumps and obstacles. Cyclocross is a form of bike racing that involves bikes with wider tires for riding on off-road terrain. Track cycling is the sport of racing bikes on a purpose-built indoor track.