Backup
A backup offer is when a home seller has accepted an offer from a buyer, but is still accepting offers from other buyers. Sellers state that they are accepting backup offers if they think the current offer may fall through.
Short Sale
A short sale is a sale of real estate in which the net proceeds from selling the property will fall short of the debts secured by liens against the property. In this case, if all lien holders agree to accept less than the amount owed on the debt, a sale of the property can be accomplished.