As per the official page of Tailwind CSS, it is a highly customizable, low-level CSS framework that gives you all of the building blocks you need to build bespoke designs without any annoying opinionated styles you have to fight to override.
To simply put, Tailwind provides helper classes for almost every CSS rule available. Fuse includes and uses Tailwind by default and it can be used in any part of the theme.
Official Tailwind CSS documentation: https://tailwindcss.com/