stylus-loader integrates the Stylus CSS preprocessor seamlessly into your webpack build process. It compiles .styl files into standard CSS, enabling you to leverage Stylus's powerful features like variables, mixins, and functions within your projects. This loader simplifies the workflow for incorporating Stylus stylesheets, allowing you to modularize and manage your CSS more effectively within a modern JavaScript environment. It's a key asset for developers who prefer Stylus and webpack.