Even though personal cheques (or checks) may not be used as widely as in the past, it remains a popular method for online casino withdrawals and deposits.
A cheque is simply a document that authorizes a bank account to pay a named beneficiary. As such, anyone using this method of payment at an online casino needs to have a current account with a bank.
The cheque has actually been used in one form or another since the 9th century, making it probably the world's oldest payment method. To have survived right from the Middle Ages to the dawn of the internet and online casinos is quite an achievement.