Have you been looking for a game and seen something like, "Mario Kart for Wii and Gamecube." But the picture to the side showed this:

It says in the top left corner of the video game: Only for Nintendo Gamecube, and across the top it says Nintendo Gamecube. By this time you're wondering, "How is it also compatible with the Wii?"

The Wii can also play Gamecube games! The same slot you slide your Wii game disk into also can hold your Gamecube disk (even though it is less than half the size). The game is unchanged and you can enjoy the excitement of a Gamecube game on the Wii. The only difference is you need a gamecube controller (NOT a wii remote OR nunchuck), the only exception is the wii classic controller which you can buy at the store. These controllers are inserted at the top of your Wii. Just simply lift up the flap on the top and plug in the controller and you're ready to go! The two slots further back that are longer and thinner in shape are for a Gamecube NOT Wii memory card.

So if you see a seller stating that a Gamecube game is also for Wii, they're absolutely right and you can buy with confidence that they're not lying.