Sass is a super set of CSS that allows to create more structured stylesheets. You can create .scss files that allows for mixins, variables, cleaner syntax, etc.

You then compiles it into a proper CSS file via the command line (it’s ruby-based).

Bonus point: a introductory blog post for you python/django-file out there: http://www.bigjason.com/blog/using-sass-django/.