Difference between v model and and v-v model

is there any difference between v model and v-vmodelif so plztellme what are the difference between them

Here's the wiki link for v-model
[url=http://en.wikipedia.org/wiki/V-Modell]V-Model - Wikipedia, the free encyclopedia[/url]

And as far as I know, there is nothing like v-vmodel.

I have heard of VV model but no docs found on net