A champion (from the late Latin campio) is the victor in a challenge, contest or competition. There can be a territorial pyramid of championships, e.g. local, regional / provincial, state, national, continental and world championships, and even further (artificial) divisions at one or more of these levels, as in soccer. Their champions can be accordingly styled, e.g. national champion, world champion.
In certain disciplines, there are specific titles for champions, either descriptive, as the baspehlivan in Turkish oil wrestling, yokozuna in Japanese sumo wrestling; or copied from real life, such as the koning and keizer ('king' and 'emperor') in traditional archery competitions (not just national, also at lower levels) in the Low Countries.
The original meaning of the word partakes of both these senses: in the Feudal Era, knights were expected to be champions and paragons of both prowess in combat and of causes, the latter most commonly being either patriotic, romantic or religious in nature (thus becoming models of virtue). This reaches its most literal meaning in a trial by combat, in which each combatant champions the cause of one side of the trial. A "King's Champion" is appointed for ceremonial purposes at the coronation of an English Monarch, to defeat any challenger to the monarch's right to be crowned.
Champion warfare refers to a type of battle, most commonly found in the epic poetry and myth of ancient history, in which the outcome of the conflict is determined by single combat, an individual duel between the best soldiers ("champions") from each opposing army.
World Champion is a title used to denote a winner of a World championship in a particular sport, discipline or game. Being a champion at any sport or game requires an extraordinary amount of focus, discipline, drive and complete dedication, usually from a young age. What separates a world champion from the average competitor aside from natural ability and environmental advantages with access to the best training facilities, is the ability to focus on their goal and to become the best of the best, the obsession to continually improve and mental conditioning required to focus on becoming the best in the world at their given subject.