Mortgage Insurance covers the mortgage lender against loss caused by a mortgagor's default. It may cover all or part of the loss and it may or may not relieve any liability on the borrowers part if default on the mortgage occurs.

Private Mortgage Insurance (PMI) was developed to help borrowers purchase a home without putting 20% down as was required by banks and lenders many years ago. I like to think of it as a "hired co-borrower". Two out of five borrowers use PMI