What is a deficiency judgment?

A deficiency judgement is a judgement that arises against a debtor when the collateral that secured the debt was a then sufficient value to satisfy the debt.
This can occur either in a real property or personal property setting.

For example, if an individual owes $100,000 on their mortgage and the property that was mortgaged is only worth $50,000, the creditor could apply to the court after the foreclosure sale for a judgement against the debtor, or the maker on the note, in an amount of the difference between the value of the property and the amount of the debt.