User blog comment:Element02/Hacked Cartridges/@comment-25164650-20140713125814/@comment-6907100-20140713165523

The gamesharek is really old. Basically it was a really huge cartridge where you had to connect your video game under it. It then let you input codes to have certain things happen in your game, like catching a Shiny Celebi or turning every Pokemon into Missingno or something. You could give yourself unlimited lives or skip to the last level...things like that.

They generally were not worth it. They would screw up the data in your game and sometimes the game would get so badly corrupted that it could no longer be played. So yeah, it was just one of those things that kids got so they could cheat. Nowadays, we use Action Replay which is not as bad, but it pretty much does the same thing.