Mid-major

Mid-major is a term used in American NCAA Division I college sports, especially men's basketball, to refer to athletic conferences that are not among the so-called "Power Five conferences" (the ACC, Big Ten, Big 12, Pac-12, and SEC), the American, the Atlantic 10, Mountain West and the Big East, the programs of which are sometimes referred to as "high majors" by comparison. The term "mid-major" was coined in 1977 by Jack Kvancz, head coach of Catholic University's men's basketball team. Such a distinction is not officially acknowledged by the NCAA, nor does the NCAA use the terms "major" and "mid-major" to differentiate between Division I athletic conferences. It is considered offensive and derogatory by some fans and schools.

Because of the development of the now-defunct Bowl Championship Series in 1998, and the lack of a playoff format for the Football Bowl Subdivision prior to the College Football Playoff, the demarcation line between major and mid-major conferences was much clearer in college football than in other sports. The six conferences of the BCS each had guaranteed appearances in one of the four major bowl games (Rose Bowl, Fiesta Bowl, Orange Bowl, and Sugar Bowl), whereas mid-majors — the teams that were not in one of those six leagues — relied on an at-large bid or a high ranking to qualify for a major bowl. (The Notre Dame Fighting Irish football team, an independent, was an exception.) It was rare for any mid-major program to receive one of two at-large bids (or only one, if Notre Dame qualified) to one of the four major bowls, even if such a program completed a perfect season. The establishment of the BCS National Championship Game opened two additional at-large berths and mandated invites for mid-major schools above a certain ranking, which led to an increase in mid-major appearances in the four major bowls. Then conference realignment brought about the end of the Big East football conference. Schools that did not join a major conference from the Big East formed the basis of the football teams in the American Athletic Conference. No mid-major ever qualified for the BCS title game. With the advent of the College Football Playoff in 2014, The American became a mid-major conference.

...
Wikipedia