The term post up in basketball refers to a player, typically the center, moving to the low post for an easy layup, dunk, or jump shot. When the center posts up, he rotates his body away from the defender to prevent a steal or block. He then takes a shot fading away, this maneuver allows him to shoot with open space as opposed to being defended.
The posts in basketball are two spots in the paint on the court. The posts are known as the high post and low post and are used by the post player to post up. The center or power forward will post up in this position in order to give their point guard a passing option.
The height advantage is one of the reasons centers and power forwards make great post players. Posting up plays are designed to take advantage of mismatches and a smaller, weaker defender. The center and power forward are known as low post players because they spend the majority of their time at the low post on the court. Low post players are great at getting rebounds, blocks, and making layups, dunks, hook shots, and jump shots near the hoop. This is a brand of the game that is somewhat dying but is still alive, specially at the college level.