Why do people specifically search for the term? Because unlike the base game, which is readily available on cartridges, the Booster Course Pass cannot be shared physically. If you buy a used copy of Mario Kart 8 Deluxe at GameStop, the DLC is locked to the original owner’s Nintendo Account.
This article breaks down exactly what the Booster Course Pass offers, the nature of the "exclusive" content within the NSP (Nintendo Submission Package) format, and how this DLC transforms the game into the ultimate Mario Kart experience. mariokart8deluxenspboostercoursepassdlc exclusive