de·fi·cien·cy /di-'fi-shən-sē/ n pl -cies: an amount that is lacking or inadequate: as
a: the difference between the amount of tax owed and the amount of tax paid
b: the difference between the amount owed under a security agreement and the amount the creditor is able to recover upon default of the debtor by selling the collateral
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.