The Nintendo 3DS Game Card is a small cartridge like item that holds a game's info. It is placed in the 3DS Game Card slot. Unlike the DS Game Cards, the 3DS Game Cards have a small tab on the top of the right side, which prevent them from being put into older DS systems. Although if one were to remove the tab, the system will not be able to detect it regardless.
The Game Card is light gray, and is roughly square-shaped, with slightly more of a curve on the bottom-left corner. The cartridge is also the same size as a Nintendo DS game card, except for a small tab on the right side which is meant to prevent it from being inserted into older DS systems. There is also a sticker on the front with the game's title on it. On the back, the contacts can be seen, and there is a model number printed onto the card. Some games, like Xenoblade Chronicles 3D, are exclusive to the New Nintendo 3DS hardware, and while standard 3DS/2DS models will recognize the games, they cannot be played on them due to slower processing speed and RAM.