Hi Shudhanshu,
In respect of your querry & as answered by abhishek, Imprest balance is like a cash balance maintained with any employee of the company to enable him to make some daily payments. However in some cases, the employee may incur expense of the amount more then the balance available with him. This may be due to some urgent payments to be made by the company which the employee may make & later recover from the company. In this case such excess payment by the employee should be recorded as current liabilities & not negtive cash balance.