Sass is a meta-language whose purpose is to be processed into CSS. The file names are actually *.scss and can be compiled by a tool like Gulp or Webpack into a minified CSS file that can be read by any browser.
Sass helps with the task of writing CSS by allowing to divide the CSS code in different files, organize it a clean structure and it gives several tools as well as a more elegant and advanced syntax. Basically, it gives more power than flat CSS allows but it does not extend the CSS standard itself as it’s CSS that will be generated from the .scss files.
