The pre-authorisation is the fee charged to your credit or debit card every day you are in a hotel to cover the cost of incidentals, such as laundry services or meals and drinks charged to your room.
It can be anywhere between $50 and $150 a night, sometimes more, and this amount is blocked from your account.
Even if you don't hit the mini-bar or use room service, it might take days or even weeks for the balance to be restored to your account, but there are ways to ease the pain.
Use a credit card rather than a debit card, otherwise it is your funds that are being used, not your credit card provider's.
When you check out, use the same card to settle your bill or it can take even longer for the funds to be restored to your account.
Anecdotal evidence suggests it may be an advantage to make a charge against your pre-authorisation, however small.
This requires the credit provider to process your payment and the outstanding balance is likely to be returned more quickly.