Japanese Mejor League is called "Nippon Professional Baseball" as NPB which is Highest level of baseball in Japan.
Locally, it is often called Puro Yakyū, meaning Professional Baseball. Outside of Japan, it is often just referred to as "Japanese baseball."
The roots of the league can be traced back to the formation of the "Greater Japan Tokyo Baseball Club" in 1934 and the original Japanese Baseball League. NPB was formed when that league reorganized in 1950.
The league consists of two six-team circuits, the Central League and the Pacific League.
Each season the winning clubs from the two leagues compete in the Japan Series, the championship series of NPB.