A cartridge is a self-contained package that holds everything needed for a particular purpose, designed to be easily inserted and removed.

Classic systems like the Nintendo Entertainment System used plastic cartridges containing computer chips with entire games stored on them. You'd slide a cartridge into the console, and everything needed to play that game was right there, ready to go. Modern systems mostly use discs or downloads instead, but cartridges were the standard for decades.

The word appears in other contexts too: printer ink cartridges hold ink, and some fountain pens use ink cartridges. In each case, the cartridge is a complete, replaceable unit. Instead of refilling or rebuilding something from scratch, you simply swap in a fresh cartridge and you're ready to continue. The genius of cartridges is that they make complex things simple: with one click, everything you need is loaded and ready.