NFV-

Network functions virtualization (NFV) allows service providers and operators to abstract network services.such as firewalling and load balancing, into software that runs on basic servers.

Network functions virtualization could replace many network devices with more flexible software running on bare metal servers.

OpenStack runs on Linux and KVM(Kernel based Virtual Machine) comes standard with all Linux distributions.KVM, the default hypervisor in OpenStack cloud software.
KVM is the virtualization layer.

NFV replaces the proprietary network elements of NEs with software that runs on standard servers. In other words NFV focuses on optimising the network services themselves.