It means Software Defined Networking
And it is to networking what virtualization is to servers. Apparently.
Google's getting more cozy with the world of SDN, opening up some of its network configuration models to give things a kick along. LightReading reports that Chocolate Factory network architect Bikash Koley wants more SDN adoption at the transport layer. To that end, the company has shared its multivendor optical terminal …
Fairly apt.
With SDN you have a single UI that manages all your switches. They are joined to the managment server like you'd join ESXi nodes to vSphere.
Instead of configuring each individual port on each individual switch like you'd configure every install of Windows by hand in a beforetime baremetal datacenter, you make configurations at a higher level. You can clone or snapshot configs, migrate configs from port to port - even across switches - or automate deployments in a Puppet-like manner. (Or use Puppet, if you want!)
Connecting to each individual switch to control them is like bashing two rocks together. It's as patently insane as manually babying each node in an entire datacenter.
So yeah, I buy SDN "is to networking what virtualization is to servers". It's not entirely accurate, but it gets the important bits across.