A swap whose notional principal amount (NPA) doesn’t vary over its tenor. Each cashflow is calculated using a constant notional principal. For example, a swap with a notional amount of $100 million will have its cashflows based on this amount between the value date and maturity date. In a fixed notional interest rate swap, the notional amount on each payment date is equal to the principal amount of the applicable tranche after taking into account all payments (if any) of principal that were scheduled to be made on or before the immediately preceding payment date.
A more complicated structure is a variable-notional swap in which the notional principal is not constant, but varies over time.
