Tailwind CSS is an open-source, utility-first CSS framework that enables developers to build modern, responsive, and highly customizable user interfaces directly within their HTML. Instead of providing pre-designed components, Tailwind CSS offers a wide range of utility classes for styling elements, such as spacing, colors, typography, layouts, and animations. This approach allows developers to create unique designs quickly while maintaining clean and reusable code. Tailwind CSS also includes features like responsive design utilities, dark mode support, and easy customization through a configuration file. Its flexibility, performance, and developer-friendly workflow have made Tailwind CSS one of the most popular frameworks for building fast and visually appealing web applications.