A Second Mortgage is a mortgage that has a secondary, or subordinate, lien position to another, first, mortgage. Like your primary or first mortgage, the holder of a second mortgage lien can forclose on your home if you default on your payments, however when this happens, the first lien must still be paid off or assumed by the second lienholder.

Examples of second or subordinate liens are the second loan in a "combo" when you purchase your home, most seller financing, most home improvement loans, and  Home Equity Lines of Credit (HELOC).