A zone defense that puts two players at the front (usually the two guards) and three players at the back (usually the two forwards and one center). It is sometimes called the "2-1-2 zone" because the middle player at the back (usually the center) may move further up towards the free throw line.
The 2-3 zone is the most popular zone defense because it is the most conservative and the easiest to teach. This defensive scheme takes away inside shots and penetrations, which then forces the offense to "shoot over the zone" from the perimeter. It's also effective at hiding individual defensive mismatches since the entire defense shifts with the ball.
Coach Jim Boeheim of Syracuse uses the 2-3 zone defense almost exclusively and has found tremendous success with it. Boeheim has been Syracuse's coach since 1976, and during his tenure he has posted a record of 856-301, leading the Orangemen to three Final Four appearances and one NCAA Tournament Championship (2003).