Cyclo-cross (sometimes cyclocross, CX, CCX, cyclo-X or 'cross) is a form of bicycle racing. Races typically take place in the autumn and winter (the international or "World Cup" season is October–February), and consist of many laps of a short (2.5–3.5 km or 1.5–2 mile) course featuring pavement, wooded trails, grass, steep hills and obstacles requiring the rider to quickly dismount, carry the bike while navigating the obstruction and remount. Races for senior categories are generally between 30 minutes and an hour long, with the distance varying depending on the ground conditions. The sport is strongest in the traditional road cycling countries such as Belgium (Flanders in particular), France and the Netherlands.
Text from Wikipedia, the free encyclopedia - http://en.wikipedia.org/wiki/Cyclo-cross