Organized Baseball is the term for Major League Baseball and its associated minor leagues. Not included are amateur leagues, most professional international leagues, the former Negro Leagues and independent leagues.
All minor leagues that are part of Organized Baseball are assigned a class - originally A through D, later expanded to include rankings such as AA, A1, AAA and Rookie leagues. The modern structure for organized baseball was originally established in 1902. However, MLB did not renew that agreement when it last expired after the 2020 season - which never saw a minor-league game because of the Coronavirus pandemic. Instead, the big leagues essentially took over the minors. As part of a Minor League Reorganization, MLB dropped affiliations from 43 teams and gave three of them to then-independent teams, thus reducing the number of teams by a net of 40, from 160 to 120. Affiliation agreements went from two pages to hundreds and parent clubs unilaterally "invited" farm teams, rather than choosing each other in the old system's biennial "Affiliate Shuffle". Schedules were completely restructured, two lower classes were dissolved the various leagues were renamed, franchises were shifted around, and generally geographic distances between parent and farm teams were reduced.
As a result of these changes, what was for decades known as Minor League Baseball is now the "Professional Development League" and Organized Baseball comprises Major League Baseball and its wholly-owned subsidiary.