Triathlon is a multi-sport event combining swimming, cycling, and running, established in the 1920s in France and first held in San Diego in 1974. It became an Olympic sport in 2000, featuring standard distances like a 1,500 m swim, 24.9-mile bike ride, and 6.2-mile run. Training for triathlons requires gradual acclimatization, proper diet, and the right gear to build stamina while preventing injuries.