Search Engine Friendly URLs/26/en
From Joomla! Documentation
The first segment of a route is, for regular URLs, the alias of a menu item. The SEF URL is said to be routed through that menu item. The other segments are determined entirely by the router of the component that provides the type of the menu item. The Category - Blog menu item type, for example, is provided by the Content component, and therefore that component's router is responsible for building and parsing the remaining segments.