This is what we found on Wikipedia regarding the FIM World Supercross Australian Grand Prix:

Grand Prix motorcycle racing is the highest class of motorcycle road racing. Events are held on road circuits sanctioned by the Fédération Internationale de Motocyclisme (FIM). Independent motorcycle racing events have been held since the start of the twentieth century, when large national events were often given the title Grand Prix. In 1949, the FIM was founded as the international governing body for motorcycle sport, and it coordinated rules so that select events could become part of official world championships. Grand Prix road racing is the oldest established motorsport world championship.

Grand Prix motorcycles are purpose-built racing machines that are unavailable for purchase by the general public and unable to be ridden legally on public roads. This contrasts with the various production-based categories of racing, such as the Superbike World Championship and the Isle of Man TT Races, that feature modified versions of road-going motorcycles available to the public.

The top division in Grand Prix racing was originally known as 500cc. Since 2002, the start of the four-stroke era, it has been known as MotoGP. The modern championship is divided into three official classes: MotoGP, Moto2, and Moto3. While 500cc/MotoGP is recognised as the premier class world championship, all classes hold official status. All three classes now use four-stroke engines.

The most successful rider across all Grand Prix classes is Giacomo Agostini, with 15 titles and 122 race wins. Agostini also holds the premier class title record, with eight championships, followed by Valentino Rossi and active rider Marc Márquez with seven each. As of 2025, Rossi holds the record for most premier class race wins, with 89.