A previously obscure, esoteric type of bicycle racing sport originating in Europe in the early 1900s. In cyclo-cross, cyclists ride a modified road-style bike through a technical course, generally off-road, and occasionally dismounting and carrying the bike over unrideable obstacles. Cyclo-cross originated as a way for riders to continue off-season training and to improve bike handling skills by encouraging riding in horrid winter conditions. Modern cyclo-cross is a huge spectator draw in countries like Belgium (it is arguably the Belgian national sport), and is one of the only forms of cycling in which the spectator can interact directly with race participants by offering "hand-ups" (often beer or food or even money) to racers. Heckling of racers is actively encouraged. Cyclo-cross has made great inroads into the USA in the last decade with many local race promoters offering cyclo-cross races and race series, with many highly-ranked US racers competing in the World Championships in Europe. It is growing rapidly in popularity as an alternative to high-speed, often dangerous road-style racing and spectator-unfriendly mountain bike racing, with lower top speeds and less dangerous terrain. The best cyclocross races are often non-serious affairs with racers in loud costumes with decorated, often silly-looking bikes.
Bob: I'm thinking of racing cyclocross this year.
Andy: Don't think about it. Just do it. It's like a mud run mixed with a time trial.
Bob: Dope.