An early form of
copy protection. The wheel was composed of a base with various symbols or words and a wheel lying on top of it with various cutouts. When asked for the code, you line up the cutouts with the symbol given and put in the code revealed by the holes. Some slightly more clever companies made the code an integral part of the game, necessary to continue past a certain point, rather than merely asking for a code and quitting if it wasn't presented. The idea was that the code wheel would be faster than flipping through pages looking for a
keyword in the manual while somewhat more difficult to copy. Of course, if it was lost or fell apart you were out of luck, but the publishers didn't really care about that. Still, people managed to copy them - I have several pages of
Life and Death code wheel pages lying around my house somewhere.
As far as I know, this was only used for computer games, as I can't quite see a business relying on spinning a cheap piece of reinforced paper in order to get their program to work. Some notable games that featured a code wheel were Monkey Island 2 : Le Chuck's Revenge with its Mix'n'Mojo Voodoo Ingredients Proportion Dial and various SSI games like Curse of the Azure Bonds.