What is a USB game cartridge?

A USB game cartridge is a game stored on a USB drive (or a device shaped like a cartridge with a USB connector) that you plug into a console to load and play that game. It is a modern, DIY-friendly take on the classic plug-in cartridge: instead of a custom chip, the game files live on standard USB storage, so anyone can make one by copying a game onto a stick. Hobby and homebrew consoles use this because it is cheap and simple, and it brings back the tactile feel of swapping physical games. Dungeon Mastron's DIY console uses exactly this idea: each story game lives on its own USB cartridge you slot in to play, though the hardware build is still in beta.