A vanilla swap which has a zero net present value (NPV). That is, it involves no initial exchange of notional principal. More specifically, the present value of the cash flows of the swap’s fixed and floating legs are equal. Therefore, in a par swap, the fixed leg is similar in concept to a fixed coupon bond priced at par, where the coupon rate is equal to the swap rate.

This implies that the swap rate in a par swap is a par yield.