Sass stands for "Syntactically Awesome Stylesheets" and is a powerful CSS extension language. Similar to LESS, Sass provides additional features and syntactical improvements over traditional CSS. Some of the main features of Sass include:

1. Variables: Sass allows the use of variables to store values such as colors, fonts, and sizes and use them at various places in the stylesheet.

2. Nesting: Sass allows nesting of CSS rules, which improves code readability and reduces the need for repetition.

3. Mixins: Similar to LESS, mixins in Sass allow the definition of groups of CSS properties that can then be reused at various places.

4. Inheritance: Sass supports inheritance of styles, allowing style properties to be inherited from one class to another.

5. Functions and operations: Sass provides functions and mathematical operations that enable complex calculations and transformation functions to be applied to values.

Sass is typically provided in two syntax variants: Sass (Syntactically Awesome Stylesheets), which uses an indentation-based syntax without curly braces, and SCSS (Sassy CSS), which uses a CSS-like syntax with curly braces. However, both variants offer the same features and can be used depending on personal preference.

Similar to LESS, Sass files need to be compiled into regular CSS files before they can be used on a webpage. There are various tools and libraries available to automate the compilation of Sass files and convert them into CSS.

LESS is a dynamic stylesheet language developed as an extension of CSS (Cascading Style Sheets). The name LESS stands for "Leaner Style Sheets," indicating that LESS provides additional features and syntactical improvements that make writing stylesheets more efficient and easier to read.

Some of the main features of LESS include:

1. Variables: LESS allows the use of variables to store values such as colors, fonts, and sizes and then use them at various places within the stylesheet. This greatly facilitates the maintenance and updating of stylesheets.

2. Nesting: LESS permits the nesting of CSS rules, improving code readability and reducing the need for repetition.

3. Mixins: Mixins are a way to define groups of CSS properties and then use them in different rules or selectors. This enables code modularization and increases reusability.

4. Functions and operations: LESS supports functions and operations, allowing for complex calculations or transformations to be applied to values.

LESS files are typically compiled into regular CSS files before being used in a webpage. There are various tools and libraries that can automate the compilation of LESS files and convert them into CSS.