SD-WAN is a centalized control over the WAN infratructure where high level policies for communications are created and the controller system takes care of deploying and implementing those policies to the WAN node devices. This is a specific implementation type of SDN.
SDN is the older more generic term for using software controllers in any type of network environment.
SDN-WAN is a no longer used original term for SD-WAN. Early on this was seen as a specific implementation of SDN so this term was applied. But pretty quickly the N was dropped and the technology just referred to as SD-WAN.
Steve Puluka BSEET - Juniper Ambassador IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP) http://puluka.com/home