The phrase "pay the mortgage" is used to describe making regular (usually monthly) payments on a home loan. A mortgage is a loan provided by a bank or financial institution specifically for purchasing real estate (like a house, apartment, or land). The property itself serves as collateral, meaning if the borrower fails to make payments, the lender can take possession of the property.

For example:

They worked hard to make sure they could pay the mortgage on time every month.

After paying the mortgage, they had less money left over for other expenses.

After paying the mortgage for 30 years, they finally own their home outright.