a payment smaller than needed or expected

the act of paying less than required

This is where monthly mortgage payments are less than the amount originally specified to pay off a mortgage by the end of its term. Some mortgages, particulary flexible mortgages, allow for a specified level of underpayment but this tends to be balanced out with overpayments at other times in the life of the mortgage

a loan or mortgage payment that is less than the amount that you should normally pay for that month.

A mortgage repayment smaller than the regular agreed sum. Some flexible mortgages have this feature, which can be useful for people with irregular income.