These teams play in 31 different conferences, which
  are classified as either major or mid-major
  conferences. The distinction is unofficial; indeed, the
  winners of all 31 conferences receive an automatic
  bid to play in the NCAA Division I Men's Basketball
  Tournament alongside 34 at-large selections.
  However, the teams from "major" conferences are the
  traditional powers and continue to dominate the
  game to this day, thanks in part to the relative ease
  they have in attracting blue-chip high school recruits.
  The major-conference teams also have the benefit of
  playing a tougher schedule, more easily garnering
  respect. Accordingly, most of the 34 at-large selec-
  tions on Selection Sunday go to major-conference
  teams. The following are currently considered to be
  the major conferences in college basketball