A world championship is generally an international competition open to elite competitors from around the world, representing their nations, and winning such an event will be considered the highest or near highest achievement in the sport, game, or ability.
The title is usually awarded through a combination of specific contests or, less commonly, ranking systems (e.g. the ICC Test Championship), or a combination of the two (e.g. World Triathlon Championships in Triathlon). This determines a 'world champion', who or which is commonly considered the best nation, team, individual (or other entity) in the world in a particular field, although the vagaries of sport ensure that the competitor recognised at the best in an event is not always the 'world champion' (see Underdog). This may also be known as a world cup competition; , for example cycling (UCI World Championships and UCI World Cups)). Often, the use of the term cup or championship in this sense is just a choice of words. Some sports have multiple champions because of multiple organizations, such as boxing, mixed martial arts and wrestling.
Certain competitive exercises do not have a world championship or a world cup as such, but may have one or several world champions. Professional boxing, for example, has several world champions at different weights, but each one of them is decided by a "title match", not a tournament. In a title match system, the championship can only be won by directly defeating the incumbent, who in turn must continue to compete to retain their title or risk forfeiture.
Still other competitions, most commonly in professional sports, may or may not have a true world championship but may designate the winners of a domestic competition to be "world champions." This is especially true of the "Big Four" major professional sports leagues in the United States and Canada; world cups and championships exist in all four of the major sports, but the domestic U.S. and Canadian leagues are generally known as the world professional championships (as with the Stanley Cup, ostensibly an independent championship for ice hockey but under the control of the National Hockey League through two dummy trustees since 1947) or the equivalent of a world club championship. In American football, although an IFAF World Championship exists, the United States is so far above and beyond the other nations it faces that the winner of the U.S.-based Super Bowl, a competition limited to the 32 teams in the National Football League, is commonly nicknamed as the world champion by the players, the press and fans alike; the NFL itself explicitly marketed the contest as a world championship in its first iterations.
Finally, certain competitions do not have a world championship or world cup, but rather hold a series of events recognised as the elite level in their field (e.g. tennis and golf have a series of four Grand Slam events recognised as the pinnacle of the game, in addition to key team events, world tour finals and the Olympic Games, though each year ITF designates a World Champion based on performances throughout the year).