Front Controller refers to a design pattern where a single component in your application is responsible for handling all requests to other parts of an application. It centralizes common functionality needed by the rest of your application. Templating, routing, and security are common examples of Front Controller functionality. The benefit to using this design pattern is that when the behavior of these functions need to change, only a small part of the application needs to be modified.
In web terms, all requests for a domain are handled by a single point of entry (the front controller).
An extremely simple example of only the routing functionality of a front-controller. Using PHP served by Apache would look something like this. Most important step is to redirect all requests to the front controller:
.htaccess
RewriteEngine On
RewriteRule . /front-controller.php [L]
front-controller.php
<?php
switch ($_SERVER['REQUEST_URI']) {
case "https://stackoverflow.com/help":
include 'help.php';
break;
case '/calendar':
include 'calendar.php';
break;
default:
include 'notfound.php';
break;
}