Symfony developers like to say that this is more than a web application framework. To them, Symfony is a set of PHP components, a framework, a philosophy, and a community. Aside from the fact that all frameworks have a philosophy and a community, the components are an important part of Symfony, as the framework is built on top of them. Basically, components are decoupled and reusable components on which apps are built.
Symfony is a PHP web application framework and a set of reusable PHP components/libraries. It was published as free software on October 18, 2005 and released under the MIT license.