In 1906, the Automobile Club de France introduced the Grand Prix to replace the unsatisfactory International Cup (or Gordon-Bennett) races, which immediately became the Gold Standard for automobile racing competition. In subsequent years, other national clubs followed suit, and started organizing big races under the names "Grand Prize", "Gran Premio", "Großer Preis" etc. to the point that the top category of auto racing became known as 'Grand Prix Racing'.
The following year, in 1907 the Auto-Cycle Union of Britain introduced the Tourist Trophy on the Isle of Man to replace the unsatisfactory International Cup races, setting a new Gold Standard for motorcycle racing competition. Would it not have been handy, even practical to have used the Grand Prix and Tourist Trophy name tags to differentiate between the top car and motorcycle competitions in each country? Yes, and it even happened - to a degree.
Some countries, like the Netherlands or Sweden, named their top motorcycle events the "Dutch TT" and "Swedish TT", respectively, even though the events have also been called Grands Prix in more recent years. Germany had a "Deutsche TT" in 1922, three years before the first "Großer Preis der Motorräder", and Austria had the "Österreichische TT" for a decade after 1923 as its biggest competition for motorcycles, outshining the "Großer Preis", held for a few years in the later twenties, and then regularly from 1950 onwards. The "Deutsche TT" lived on until at least the early nineties, though it became a mere 'international' in later years, often even held on the rather pathetic (for an event named Tourist Trophy!) Betonschleife of the Nürburgring.
Most of the Anglosaxon countries also used the TT name to an extent, and there were the "New Zealand TT" (not sure if there was ever an NZ GP for bikes?) and "Australian TT" in the thirties already. Australia soon confused the matter, and for many years there were Oz GPs and TTs rivalling each other, often with alternating venues to really make your head spin - I will try to entangle that in a seperate thread, soon. The USofA basically named every race on a track with a right turn a "Tourist Trophy", and would eventually create the "Steeplechase TT" as its own category, much closer to what we now call Motocross, but not the same!
Italy and Spain used the TT moniker sparingly, and I'm not sure if it was ever used in official race names, while France and other French speaking countries eschewed it entirely - already in 1912, both major French motorcycle clubs organised Grands Prix for two- and three-wheelers, and that's the way it stayed in Belgium, too. And let's not forget that the British themselves followed the French guideline when looking for a name for Ulster's biggest motorcycle race of the year in 1922!