Struts is an open-source framework used for building web applications in the Java programming language. It follows the Model-View-Controller (MVC) design pattern, which helps separate the application logic from the user interface. This separation makes it easier to manage and scale applications, as developers can work on different components independently. The framework provides a set of tools and libraries that simplify the development process, allowing developers to create dynamic web pages more efficiently. With features like form handling, validation, and internationalization, Struts helps streamline common tasks in web development, making it a popular choice for many Java-based projects.