Explain Friendly URLs?

In Liferay instead of showing entire portlet URL in browser we can define friendly URLs for each portlet

we have to define three elemnts  liferay-portlet.xml.

■ Mapper class
■ Mapping
■ Route

In almost all cases , Mapper Class is
com.liferay.portal.kernel.portlet.DefaultFriendlyURLMapper

The mapping is a name by which this route can be identified, and the route is a file
that describes how to map various parameters to a more friendly look