There are also hotels/merchants who may ask for a deposit or holding amount when trying to book a reservation. Said amount will be automatically debited from your card balance too. Reversal of said amount or any amount determined by the merchant/hotel will happen after you check out of the hotel.
For example, if you are reserving a hotel booking on September 13, the hotel may ask for a holding amount of 500 AUD. 500 AUD will be instantly debited from your card. Then by September 14, after your check, out, 500 AUD or less (if the hotel charges you additional fees against this deposit) will be returned back to your card balance.