Thymeleaf is a modern server-side Java template engine for web and standalone environments. It enables developers to create dynamic web pages with natural templates. Thymeleaf templates can be seamlessly integrated with Spring Framework to build web applications, although it can also be used in standalone applications. Thymeleaf also provides extensive support for processing and manipulating HTML, allowing developers to easily add dynamic content, iterate over collections, conditionally display elements, and perform other common tasks directly in the templates.