Mediator in PHP
Mediator is a behavioral design pattern that reduces coupling between components of a program by making them communicate indirectly, through a special mediator object.
The Mediator makes it easy to modify, extend and reuse individual components because they're no longer dependent on the dozens of other classes.
Usage of the pattern in PHP
Usage examples: The pure implementation of the Mediator pattern isn't as common in PHP, as it's in other languages, especially GUI-targeted like Java or C#. A PHP application may indeed contain dozens of components, but they rarely communicate directly within a single session.
However, there are still uses for the Mediator pattern like the event dispatchers of many PHP frameworks or some implementations of MVC controllers.