The term "deficiency judgment" refers to a judgment for a debt, the amount of which is the shortfall that is created after foreclosure when the collateral taken back by the lender has a current market value that is less than your current debt to the lender. The law permits the lender to come back for the remainder because it was not made whole by the acquisition of the property
Therefore, it would be the difference between your current debt and the value of the property.
The deficiency is calculated by adding all the costs associated with the foreclosure, including the amount still owed to the bank, attorney's fees, court costs, interest, etc. and subtracting the amount the house sold for at auction. Whatever is left is the amount the court can enter as a deficiency judgment.