In casino terminology, the term rack refers to a tray used to hold and carry slot machine tokens, casino chips, and coins. The tray is usually made of clear plastic so the players can’t use them to cheat and hide cards and other forbidden items.
Its purpose is to make players’ lives easier since casino chips are usually sold in the smallest denominations. This means that a player can often have dozens or even a hundred casino chips to carry around.
Therefore, instead of carrying chips around and potentially losing some, you can simply put them in a chip rack. Consider it a wallet for casino chips. Once you run out of chips, instead of going to the casino cage, you can simply request a new rack from the dealer.
In addition, a rack usually has five different compartments, so that players can separate the chips by their denomination.