Ducati Desmosedici is the name of the series of four-stroke V4 Prototype Motorcycles developed by Ducati to compete in the MotoGP World Championship. GPx indicates the version of the bike, where x corresponds to the year the bike raced (i.e. the Desmosedici GP9 raced in 2009).
Read more about Ducati Desmosedici: Background, Desmosedici RR