X synchronization

X Synchronization - A feature on a flash cord/camera that allows simultaneous triggering of a shutter and a flash unit.

- Y - ...

flash may be all over before the shutter gets open. To fire electronic flash with a focal-plane shutter, the switch in the camera is closed at the instant the first curtain of the focal-plane shutter reaches fully open-called X synchronization.

See also: Hood, Mode, Negative, Synchronization, ED lens