https://en.wikipedia.org/wiki/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 10, Big 12, Pac-12, and SEC), the Big East, the American, the Atlantic 10, and the Mountain West. These conferences are sometimes referred to as "high majors" by comparison.'
'Typically, the term is used to refer to teams that are members of a conference other than the Power Five. Others believe the term uses an arbitrary litmus test, based on how many teams from a given conference qualify for the NCAA tournament in a "good" year, or how much success a given conference has had in the NCAA tournament, or even conference revenue and attendance. The Big East Conference and the American Athletic Conference are not in the Power Five, but are almost always considered high major conferences. Also sometimes branded as high majors are the Atlantic-10 Conference, and the Mountain West Conference.'
'Until the last decade, the Atlantic 10, Conference USA, the Mountain West Conference, and the Western Athletic Conference were widely considered to be above the level of the other "mid-major" conferences, but still generally below the level of the five major conferences. However, due to recent changes in membership in some conferences, as well as the sustained success of some "mid-major" conferences, most no longer consider the Atlantic 10 and Mountain West to be below the level of the CFP [college football playoff] conferences in college basketball.'
'Note that some [designated mid-major] conferences, including the Mountain West, American Athletic Conference, and the Atlantic 10, may be considered a "high-major" as opposed to a mid-major depending on whom one asks.'
'The basketball website Collegeinsider.com created its own definition of "mid-major" when it introduced a pair of end-of-season awards for outstanding mid-major individuals in college basketball: the Lou Henson Award for players (first presented in 2010) and Hugh Durham Award for coaches (first presented in 2005). Since the 2013–14 season, players and coaches from the following conferences have been ineligible for these awards:
All conferences that sponsor FBS football, except for the MAC and Sun Belt;
Atlantic 10;
Big East;
Members of these conferences are also generally ineligible for the CollegeInsider.com Postseason Tournament.'