A decathlon has 10 events, a heptathlon has seven, and a triathlon has three. The biathlon, then, has just two. And an odd couple they are: cross-country skiing and shooting.
This eccentric competition has been contested in various forms since the 18th century and has been part of the Olympics since 1924 (when it was known, more descriptively, as the military ski patrol).
Modern Biathlon is a standard cross-country ski race with periodic interruptions in which the athletes pull a .22-caliber rifle off their backs, point it at a target and shoot. Missed targets cost time and sometimes require racers have to ski a 150-meter penalty lap.