I have been hammering on how unclear the definition of SDN has been until today and how every vendor is stretching that to do some SDN–washing of their products. Jason Edelman wrote a definition down during the Open Networking Summit.
It is the definition by Nick McKeown, Professor at Stanford, co-founder of Nicira, Board Member at the Open Networking Foundation (ONF).
SDN has two properties (1) physical separation of the control plane and data plane and (2) a single controller (control plane) can control multiple devices.
I think it is a very clear definition, which does not include Network Functions Virtualization. I propose to stick with this one.