Your mortgage company determined that they couldn't recover what you still owe on your mortgage because of foreclosure, abandonment, or because you relinquished your property to them.
They are therefore canceling or forgiving a portion of your debt, which is usually the difference between what you owed and the home's fair market value or the gross foreclosure bid.
This gets reported on Form 1099-C. Your canceled debt will be in Box 2, and your home's fair market value is in Box 7. Contact your lender if you don't agree with the amounts.
You might not have to pay taxes on the Box 2 amount if you qualify for mortgage debt relief (tax years 2007-2017 only). We'll figure out if you qualify for relief after you enter your 1099-C.