Previous Olympic Games included sports that are no longer included in the current program, such as polo and tug of war. Known as "discontinued sports", these have been removed due to either a lack of interest or the absence of an appropriate governing body for the sport. Some sports that were competed at the early Games and later dropped by the IOC, have managed to return to the Olympic program, for example Archery, which made a come-back in 1972, and tennis, which was reintroduced in 1988. The Olympics have often included one or more demonstration sports, normally to promote a local sport from the host country or to gauge interest in an entirely new sport. Some such sports, like baseball and curling, were added to the official Olympic program (in 1992 and 1998, respectively). Baseball was discontinued after the 2008 Olympics in Beijing, only to be revived again for the forthcoming 2020 Olympics in Tokyo, which will see the introduction of new disciplines within a number of existing Summer Olympics sports as well as several new sports, such as karate and skateboarding, making their Olympic debuts.
The term "sport" in Olympic terminology refers to all events sanctioned by an international sport federation, a definition that may differ from the common meaning of the word "sport". One sport, by Olympic definition, may comprise several disciplines, which would often be regarded as separate sports in common usage.
For example, aquatics is a summer Olympic sport that includes six disciplines: swimming, synchronized swimming, diving, water polo, open water swimming, and high diving (the last of which is a non-Olympic discipline), since all these disciplines are governed at international level by the International Swimming Federation. Skating is a winter Olympic sport represented by the International Skating Union, and includes four disciplines: figure skating, speed skating (on a traditional long track), short track speed skating, and synchronized skating (the latter is a non-Olympic discipline). The sport with the largest number of Olympic disciplines is skiing, with six: alpine skiing, cross-country skiing, ski jumping, nordic combined, snowboarding, and freestyle skiing.
Other notable multi-discipline sports are gymnastics (artistic, rhythmic, and trampoline), cycling (road, track, mountain, and BMX), volleyball (indoors and beach), wrestling (freestyle and Greco-Roman), canoeing (flatwater and slalom), and bobsleigh (includes skeleton). The disciplines listed here are only those contested in the Olympics—gymnastics has two non-Olympic disciplines, while cycling and wrestling have three each.
It should also be noted that the IOC definition of a "discipline" may differ from that used by an international federation. For example, the IOC considers artistic gymnastics a single discipline, but the International Federation of Gymnastics (FIG) classifies men's and women's artistic gymnastics as separate disciplines. Similarly, the IOC considers freestyle wrestling to be a single discipline, but United World Wrestling uses "freestyle wrestling" strictly for the men's version, classifying women's freestyle wrestling as the separate discipline of "female wrestling".