7 - Sass Mixins

Mixins allow you to define styles that can be re-used throughout the stylesheet without needing to resort to non-semantic classes like .float-left. Mixins can also contain full CSS rules, and anything else allowed elsewhere in a Sass document. They can even take arguments which allows you to produce a wide variety of styles with very few mixins.

http://sass-lang.com/documentation/file.SASS_REFERENCE.html#mixins