A slang term for a type of basketball player who consistently rebounds at a high rate. A player who rebounds a lot is one of the most valuable players on a team, since he can increase possessions and second-chance points. This phrase is complimentary and is usually, though not always, reserved for one player on a given team. This is the result of most teams only carrying one starting center-the de facto rebounder on the court-on their rosters.
This term comes from the fact that backboards in the NBA have been made of glass for more than 50 years. When a shot misses, it typically bounces off the backboard at some point, which is why a player who rebounds is also known as one who "cleans the glass". Some NBA players known for being great rebounders are Dennis Rodman, Ben Wallace, David Robinson, and Tim Duncan.