As the name suggests, triathlon is an event which consists of three sporting events, which require a lot of endurance, fitness, and stamina. It includes cycling, swimming, and running. All these need to be done in succession, and over different distances. The one who completes all three first, including the changeover time, is the winner. But, the overall duration of a triathlon differs according to the type it is, and the three main types of triathlons are Olympic, Sprint, and Ironman. The International Triathlon Union (ITU) and World Triathlon Corporation (WTC) are the two major governing bodies for triathlon events all over the world.
The Olympic triathlon is characterized by 1.5 km of swimming, 40 km of cycling, and 10 km of running. Another name for this is 'International Distance', or 'Standard Course', or 'Short Course'.
Beginning with a 750 meter swim, a sprint triathlon includes 20 km of cycling, followed by a 5-km run. However, the swimming distance may vary here. There is another type of sprint, which is the 'super sprint', and has even lesser distances in each of the three events.
This is also called the 'Long Distance Triathlon', or a 'Long Course Triathlon', and is sanctioned by the International Triathlon Union. It is organized by the WTC. As the name goes, it surely needs an extremely fit and strong athlete to carve a niche in this type of event. It is a task which can be accomplished by nothing less than an ironman, literally speaking. In this type of triathlon, if it's a full triathlon, there is a 3.8-km swimming stretch, succeeded by 180 km of cycling, and ends with a 42.2-km stretch of running, which is marathon standard. If it is a half event, then all the distances―swimming, cycling, and running are reduced to half. It is also called 'Half Ironman'. However, the most prestigious one is the 'Ironman Hawaii'. It includes 3.86 km of swimming, 185.07 km of cycling, and a Honolulu Marathon.
There are few others that are sponsored by the ITU, which are longer than the standard course. There is a triathlon called 'Double Olympic', which has 3 km of swimming, cycling for a distance of 80 km, and running for 20 km. This is also termed as 'O2' or long distance. 'Triple Olympic' is another variant, called 'O3', which is 4.5 km of swimming, 120 km of bike riding, and running for 30 km. There are also the shorter variants which are specially for novices and young athletes.