A reverse mortgage is a loan. You are borrowing against your home equity. However, unlike traditional mortgages, with a reverse mortgage you do not have to pay back the money borrowed as long as you are living in the home.
When you get a reverse mortgage, you are borrowing your own home equity. (Home equity is the difference between what your home is worth and the amount you owe on your home.) So if your home is appraised at $300,000 and you still owe $50,000 on the mortgage, then you have $250,000 in home equity.