instruction: What is a triathlon?
output: A triathlon is a sport that combines three different events: swimming, biking and running, in that order. The reason for the order of events is that they proceed from more to less dangerous, so that the triathlete (as a triathlon participant is called) is most fresh and well-rested when they swim (so as to avoid drowning) and most exhausted during the run, when it is relatively less dangerous to make a mistake than it would be in the water or on a bicycle. Triathlons differ based on distance and terrain. They can be as short as a sprint event, which might include a swim as short as a single lap in a pool, or as long as an ironman triathlon, which includes a 2.4-mile swim, 112 miles of biking, and a full marathon. A common triathlon distance in between a spring and ironman is the olympic triathlon, which includes a 1.5-kilometer swim, 40 kilometer bike ride, and 10 kilometer run. Triathlons can take place anywhere where it is possible to do all three activities, including near a swimming pool, lake or open ocean. The run is most commonly done on a hard asphalt surface but can also take place on a dirt trail.