The plus-sign shaped 'button' on an
NES controller used for directional movement. Some people find that the crosskey is a source of horrible blisters on their thumb, but video game companies continue to put them on their controllers, including the
Game Boy,
Virtual Boy,
Super Nintendo,
Nintendo 64, and
Dreamcast. Similar (but not quite identical) devices can be seen on the
Genesis, which had something shaped like a crosskey molded onto a circular "D-pad," filling in the diagonal space and making the controller supposedly less painful to use, and the
Playstation, which looks as though it actually has four separate buttons for its directional movement, but they are all part of the same piece of plastic. No one really knows why Sony designed the controller this way, but it's generally considered even more painful to use than a normal crosskey.
Prior to the release of the NES, a
joystick was considered the standard controller for a home video game. The
Intellivision had a circular "disc" controller, but this was generally considered weird, and recieved enough complaints that Mattel eventually marketed a snap-on joystick to go over the disc. In 1985, though, when
Nintendo was trying to convince retailers to carry the NES, they knew stores would be reluctant about anything resembling
older video games, so, amongst other things, they decided to release it with the crosskey, and it caught on.