Sass versus LESS

Quoting, "One of the hot new trends in web design is CSS pre-processed languages and there’s two big ones vying for your attention—LESS and Sass. LESS and Sass are both ways of writing CSS code with a syntax that allows you to use features not yet available with Cascading Style Sheets (CSS), such as variables, nesting, conditionals, and more.

Pre-processed CSS languages add features to CSS that aren’t there yet—like variables, conditionals, and functions. They’re called pre-processed, because their final step is a processing, also called compiling, that converts the pre-processed language to regular CSS. In a nutshell, what you use on your site ends up being plain vanilla CSS, but comes as a result of processing the LESS, Sass, or other pre-processed language files you create." via blog

Review links— has modules on the topic—