A blank check is a term used to describe an authorization or permission given to someone to do something without any restrictions, limitations, or conditions. It means that the person has complete freedom and discretion to act as they see fit within certain boundaries. The phrase can also refer to a written order for payment of money, where the amount is left blank and the payee fills it in later. In this sense, it represents an unlimited authorization to make a payment without any restrictions or limitations on the amount.