Basically, a framework consists of:
A toolbox - a set of prefabricated, rapidly integratable software components. This means that you will have to write less code, with less risk of error. This also means greater productivity and the ability to devote more time to doing those things which provide greater added value, such as managing guiding principles, side effects, etc.
Best Practices guaranteed! A methodology – an “assembly diagram” for applications. A structured approach may seem constraining at first. But in reality it allows developers to work both efficiently and effectively on the most complex aspects of a task, and the use of Best Practices guarantees the stability, maintainability and upgradeability of the applications you develop.
And although it might be obvious, we thought it best to say it anyway – Symfony is a PHP framework, which means that it permits web applications to be built in PHP!
Detailed info about Symfony: https://symfony.com