What is KML?
Keyhole Markup Language, abbreviated KML, is a markup language for geodata. Simplified explained, one or more coordinates are not displayed on a map but stored as text-based data. Due to its small size, this file format is easier to save and transfer and can contain geodata in vector as well as in raster form.
Other maps or navigation interfaces can then display information from the KML file on a map. It became known through Google Earth, where KML files were created.