A championship (tournament) is a particular kind of tournament, so it has a narrower meaning than tournament. A tournament is generally used for any type of competition in which,, on one day or a few days, teams come together to compete. The winner of the tournament may be called the champion, but you would not necessarily call the tournament a championship tournament. Usually, championship tournaments refer to competitions at the end of a long season of games, during which the best teams in a league compete to determine who should be considered the overall champion of the league.