1) Payment 2) The act of paying too much 
The difference between your regular monthly repayment and a higher amount that you choose to pay. 
The situation whereby more than the required amount (i.e. the monthly repayment) is paid to the lender in order to decrease the term of the mortgage, this can be in the form of a lump sum or regular monthly overpayments.
a payment to your mortgage lender greater than the agreed amount in order to pay off the loan earlier.When monthly payments to a mortgage are increased so that the mortgage is repaid before the end of the mortgage term. Flexible mortgages allow overpayments to be made without penalty allowing significant interest savings over the mortgage term.
[n] - a payment larger than needed or expected 2. [n] - the act of paying too much
noun the act of paying too much