JSF is a component-based, server-side Java framework for developing user interfaces. It is the primary web framework in Java EE and includes the MVC model and the template framework.

It aims to simplify the frontend aspect of Java Enterprise applications and accelerate user interface development. It uses a component-based model to build the user interface. It defines a UI component model, which is bound to a well-defined request processing model, a POJO (Plain Old Java Object), in an enterprise application. This allows JSP custom libraries to handle those UI components and provides a mechanism to extend the standard UI components.

JSF saves the state information of the UI components and repopulates them during the display, since the state of the components lives beyond the lifespan of the HTTP request.

JSF operates by providing functionalities such as data conversion and component rendering. JSF doesn't change the basic page life cycle, in which a client makes an HTTP request and the server responds with a dynamically generated HTML page.

JSF is a standard framework for building presentation tiers for web applications. It provides a set of presentations and user interface components. It also provides an event model for wiring the interactions between the UI and the application objects.

Using JSF, we can build reusable components with Facelets. We can also use standard APIs, such as Bean validation, CDIs, and tag libraries.

JSF also supports HTML 5 and Ajax calls. It additionally has Faces Flow, which allows us to create business workflows, wizards, and sets of pages.