A document that is registered on your deed to show that your property has been put up as security for a mortgage loan.
Many people use the word mortgage to refer to a mortgage loan.
In fact, the word mortgage refers to the security interest in the property. The owner of a property gives a mortgage to the lender, meaning, they give the lender an interest in the property as security for the loan. In exchange for that mortgage (security), the lender grants the mortgage loan to the property owner.