Npb
In short
The Nippon Professional Baseball league is the highest level of professional baseball in Japan.
In plain words
It is a major sports league made up of twelve teams. These teams are split into two separate leagues called the Central League and the Pacific League.
A simple example
A fan might travel to Tokyo to watch the Yomiuri Giants play a match at the Tokyo Dome.
Why it matters
It is one of the most popular sports leagues in Asia. Many talented players use the NPB as a stepping stone to reach Major League Baseball in the United States.
Easy to mix up
Do not confuse it with MLB, which is the professional baseball league based in North America.