From ATT Open Sourcing Its SDN Management Platform:
... a software-centric environment that includes such technologies as software-defined networking (SDN) and network-functions virtualization (NFV), both of which are aimed at creating software-based networks that are more programmable, scalable and agile than traditional networks based on hardware. NFV puts such networking tasks as load balancing, routing, and intrusion detection and prevention into software, while SDN puts the control plane for those virtual network functions (VNFs) into software.
But to get into a long example:
SDN-NFV Reference Architecture from Verizon Network Infrastructure Planning:
‘Software defined networking’ (SDN) and ‘network function virtualization’ (NFV) are two promising concepts developed in the telecommunications industry. SDN is based on the separation of control and media planes. The control plane in turn lays the foundation for dynamically orchestrating the media flows in real-time. NFV, on the other hand, separates software from hardware enabling flexible network deployment and dynamic operation.