Windows Thin PC - clarification

I am trying to understand what Windows Thin PC is exactly?  It seems it's software I install on a computer that gives the user access to a stripped down and locked down Windows 7 setup.  However there are all kinds of references to VDI with it so I'm not sure if there's a server element involved?  For instance it discussing licensing there's this phrase that MS uses to describe Thin PC - "And since these PCs retain their existing SA coverage, they do not need any additional Windows Virtual Desktop Access (VDA) licensing for Microsoft Virtual Desktop Infrastructure (VDI) Suites." It's the VDI business in that sentence that makes me curious - as I thought VDI was server-related - Windows 7 images that you tossed out from a server via RDS/TS. So do I have to build some kind of server-based Windows 7 image in order for Thin PC to work?  And given that I can have clients access Windows 7 images through RDS/TS or can just give people pure RDS/TS sessions in XP, what would Windows Thin PC buy me?

Elucidation would be appreciated.