PHP is a popular general purpose scripting language that is especially suited to web development. Fast, flexible and pragmatic, PHP powers everything from your blog to the most popular websites in the world.
The frontend is the content management application. It enables writers, editors, and project managers to work seamlessly without the need to code. The backend is the content delivery application, which is used for publishing and displaying the content in various formats based on the CMS.
The PHP language evolved without a written formal specification or standard until 2014, with the original implementation acting as the de facto standard which other implementations aimed to follow. Since 2014, work has gone on to create a formal PHP specification.
Instead of building your own system for creating web pages, storing images, and other functions, the content management system handles all that basic infrastructure stuff for you so that you can focus on more forward facing parts of your website.