Anyone who has had a debt cancelled or forgiven in the past fiscal year should use the 1099-C tax form to note this. The lender has an obligation to send the borrower the form, and the borrower has an obligation to file it with their other tax paperwork.
Because of the housing crisis that occurred between 2007 and 2017, if you have a mortgage debt forgiven, you can exclude it from your taxable income in the following circumstances:
The debt does not exceed $2 million, provided you were married and filing jointly
The debt does not exceed $1 million, provided you had a single or married and filing separately status
Your mortgage debt was forgiven through the use of a mortgage restructuring
Your home was foreclosed upon
These circumstances are outlined in the Mortgage Forgiveness Debt Relief Act, which Congress passed in 2007.