A preprocessor is a program that takes one type of data and converts it to another type of data. In the case of HTML and CSS, some of the more popular preprocessor languages include Haml and Sass, Less . Haml is processed into HTML and Sass, Less are processed into CSS. CSS is primitive code which is made more readable and productive and easy ro maintain using these pre-processors. We can also use other features using these pre-processing languages: 1. Declare Variable to associate with color 2.Use if/else statements 3.MIxin files 4. Nesting. 5. Imports 6.Loops 7.Math