This blog post from CoG talks about vignettes; it doesn’t give a solid definition, but it does give lists of examples and discusses CS game structure generally. It’s followed by this article, and then this one, which discusses some methods for writing vignettes.
They’re oldish posts, 2010, so not everything may be current, but hopefully some of it will be helpful.
You can view the code of any of the free CoG games (or any games which you own), depending on which platform you are using; detailed instructions are here.