GPX (the GPS eXchange Format) is a data format for exchanging GPS data between programs, and for sharing GPS data with other users.
It is an XML based standard, which makes it an open format that can be read by any application programmed to do so. This makes It possible for data to be exchanged between difficult applications, even running on different platforms such as Windows, Linux, MacOS etc.
By publishing our GPS data in this format, we are making it available to users of various makes of GPS such Garmin, Magellen etc. GPX files can be loaded by popular applications such as Google Earth and Garmin Mapsource. The descriptive XML text can also be viewed by any XML or text editor and applications such as Microsoft Word and Excel. Check if your application supports the GPS format.
More information can be found on the official GPX website.