Wikipedia defines a short sale as the following,
“A short sale is a sale of real estate in which the sale proceeds fall short of the balance owed on the property’s loan. It often occurs when a borrower cannot pay the mortgage loan on their property, but the lender decides that selling the property at a moderate loss is better than pressing the borrower. Both parties consent to the short sale process, because it allows them to avoid foreclosure, which involves hefty fees for the bank and poorer credit report outcomes for the borrowers. This agreement, however, does not necessarily release the borrower from the obligation to pay the remaining balance of the loan, known as the deficiency”
A short sale comes by as an assured relief, whereby you can sell your home to someone at a price lower than the mortgage balance (or, less than the loan balance).