[quote name='king9x']WTF is a 'repros'? I gather physical copies of illegal software, but 'repros?'
Reproductions? Is that an actual used slang word in the "scene"?[/QUOTE]
A reproduction cart is essentially a bootleg copy of a game. There are licensed reproductions, but it seems to me that quite a lot of them are done without the knowledge or consent of the copyright holders. There are also fan-made original games and hacks of licensed games which are new or remixed games using licensed assets.
Often times they use "donor carts" to use the board from one game and to make it play another game. Sometimes they use totally new parts or a mixture of original and new parts.
Reproduction carts are often of games that never made it to the United States, fan-translations of Japanese-exclusive games and extremely rare games like Nintendo World Championships.