WGS-84 (World Geodetic System 1984): Terrestrial Reference System at world-wide level.
ED (European Datum): Terrestrial Reference System at European level.
GPS (Global Positioning System): System formed by a constellation of satellites dedicated to navigation and positioning. Receivers GPS determine the position where they are. In their configuration options it is possible to specify the datum (by default in WGS-84).
Official Map: Each country adopts a specific one. Datum is indicated in its legend.
Nautical Chart: Map used for navigation, that represents the coast and the seafloor. Datum is indicated in its legend.