A cancelable swap provides the right to cancel the swap at a given point in the future. An example would be a swap with a tenor of 5 years that can cancelled after year three. This can be broken into two components. The first is a vanilla five year swap paying floating and receiving fixed. The econd component is a payer swaption exercisable into a two year swap three years from today. The result is that when the original bond is called, the swaption is exercised and the cash flows for the original swap and that from the swaption offset one another. If the bond isn’t called, the swaption is left to expire.