The Geneva stop is named after the Geneva cross, a similar shape to the main part of the mechanism.

The Geneva stop is used to provide intermittent motion, the orange wheel turns continuously, the dark blue pin then turns the blue cross quarter of a turn for each revolution of the drive wheel.
The crescent shaped cut out in dark orange section lets the points of the cross past, then locks the wheel in place when it is stationary.

The Geneva stop mechanism is used commonly in film projectors to move the film on one frame at a time.

There is more information on Geneva Stops at the Tangen Drives website, a US company that makes geneva stops for the real world.