Thymeleaf is a modern server-side Java template engine designed for web and standalone environments. It allows developers to create web applications with dynamic and easily maintainable user interfaces. Thymeleaf offers features such as natural templating, which enables the templates to be directly viewed in a web browser without rendering, thus making the development process more efficient. It supports XML, XHTML, and HTML5 for templating and integrates seamlessly with Spring MVC. Thymeleaf is open-source and provides a plethora of features such as internationalization, form binding, and fragmentation, enhancing both the development workflow and the end-user experience.