What the Funk is GPX?
GPX (the GPS Exchange Format) is a XML data format used to exchange GPS data (waypoints, routes, and tracks) between applications and Web services on the Internet.
Put simply it is a way for your GPS to transfer GPS type info' to other devices and applications.
In this situation we provide our routes in GPX format which your GPS device can read. And similarly when you upload a route to our site your GPS device provides that route in GPX format.
You can read more about it ... here