You did not mention at what level of Baseball you are asking. But in every level there is a playoff system. Most levels from Little League to the Major League it is called the World Series. In the Major Leagues the World Series is determined by a best-of-seven game series between one American League team and one National League team. Whoever wins 4 games first wins the World Series.
Championship Baseball was created in 1986.
Championship Baseball happened in 1986.
European Baseball Championship was created in 1954.
UAAP Baseball Championship was created in 1938.
Oceania Baseball Championship was created in 1999.
Asian Baseball Championship was created in 1954.
SAARC Baseball Championship was created in 2011.
Korea Baseball Championship was created in 1982.
World University Baseball Championship was created in 2002.
Australian Schools Championship - baseball - was created in 1989.
Triple-A Baseball National Championship Game was created in 2006.
Japanese High School Baseball Championship was created in 1915.