It's important to know the differences between SDN and SD-WAN because while they both begin with SD, they are not the same. Their shared background in the separation of the control and data planes allows both to run on commodity x86 hardware. Both can also be virtualized.
SD-WAN provides software-defined application routing to the WAN and connecting an organization's' many locations.
SDN focuses internally within the LAN or the core network of the service provider. For more details: mpls vs sdn