The amount borrowed or remaining unpaid. The part of the monthly payment that reduces the remaining balance of a mortgage.
One of the terms you're likely to hear when you talk about a mortgage with your lender is principal. The principal is the amount originally borrowed or the amount that remains to be paid once you have started making payments. It is also the part of the monthly mortgage payment that reduces the remaining balance of a mortgage.
The principal balance is the outstanding amount of principal on a mortgage; it does not include interest or any other charges.