Although casino accounts are very different from bank accounts, some players treat them similarly. If they leave money in their account, they expect to find it later, even if they have not played for a long period of time.
Dormant accounts are accounts that haven't been used by players for a certain period of time. After a certain number of days (e.g. 180 days) of inactivity, some casinos gradually confiscate the money left in the accounts of inactive players.
Casinos are not banking institutions and have certain costs associated with keeping money in player accounts for prolonged periods of time. They deduct money from dormant accounts to cover these costs. However, there are also casinos that knowingly use the 'dormant accounts' clause to earn extra money at the expense of players who might have forgotten that they left some money in their casino account.
However, while most casinos have an "inactive accounts" clause, not all of them enforce it. Some casinos will return all money to their players, even after years of inactivity.
Deducting money from players' accounts is a common practice in online gambling. Although casinos are not obliged to keep account balances that are not being used for long-term gambling, a fair casino should wait a reasonable period of time (e.g. a year) before taking any action. And, it should use all means at its disposal to inform players that it will do so.
The amount of money deducted from a player's account should also be reasonable. Money should never be withdrawn in one sitting, unless the player has only a few cents in his account. Ideally, the casino should withdraw a fixed, reasonably low amount each month. However, if the remaining balance is less than the minimum withdrawal limit, it is acceptable to confiscate it.