SASS (Syntactically Awesome Stylesheets) and SCSS (Sassy CSS) are like CSS on steroids, adding the power of variables, mixins, and other enhancements to the already powerful CSS language. Written by Hampton Catlin of San Francisco, this is one of my favorite things about the web, and exciting technology. SCSS is essentially SASS with a bit more of a standard CSS-way of writing the code.
Team Treehouse has a delightful guest speaker teaching SASS: None other than Hampton Catlin, himself: get it "right from the horse's mouth!"
Andrew Chalkley has an excellent blog post that explains SASS in more detail, if you'd like to investigate a bit further.