What is LESS
LESS is a CSS pre-processor, meaning that it extends the CSS language, adding features that allow variables, mixins, functions and many other techniques that allow you to make CSS that is more maintainable, themeable and extendable. (Learn more: http://lesscss.org/)
LESS Usage in Expose
Expose framework has Built-in LESS support. You can write LESS code directly. Template LESS style files located in Template less folder.
You have to Enable LESS compiler from template admin to compile LESS files.