Tailwind CSS is a utility-first CSS framework that provides a set of pre-defined CSS classes to make styling a website faster and more efficient. It allows developers to easily create custom designs without having to write custom CSS. Tailwind CSS has gained popularity in recent years because of its flexibility, ease of use, and its ability to reduce the amount of custom CSS code required for a project. It is often used in combination with other front-end frameworks such as React, Vue.js, and Angular. Tailwind CSS includes a large number of pre-designed classes for common design patterns such as typography, grid layout, and responsive design, which can be customized and extended as needed.