This document introduces LESS, a dynamic stylesheet language that extends CSS by adding features such as variables, nested rules, mixins, functions, and operations. LESS compiles to regular CSS, allowing it to be widely supported. Key features covered include variables, nesting, mixins, functions, and guard expressions to add logic. Advantages of LESS are listed as increased organization, readability, and decreased code through its features. The document also provides information on using LESS both client-side and server-side, as well as references for further reading.