X setting

X SETTING - Shutter speed setting at which flash synchronization occurs. For some manual cameras, the X setting designates the maximum shutter speed at which the camera synchronizes with flash.
X-SYNC - Same as "X Setting" ...

X setting (X sync)
is the setting that causes the flash to burst in synchronization with the shutter. For some manual cameras, the X synch speed refers to the maximum speed that the camera can synchronize with the flash.

There are two types of synchronization: Front-Curtain Sync, which fires the flash at the start of the exposure, and Rear-Curtain Sync, which fires the flash at the end of the exposure. Also see "Rear-Curtain Sync", "Front-Curtain Sync", "X setting".

Front-Curtain Sync (first curtain), which fires the flash at the start of the exposure, and Rear-Curtain Sync(second curtain), which fires the flash at the end of the exposure. Also see "Rear-Curtain Sync", "Front-Curtain Sync", "X setting".

See also: Flash, Synchronization, Camera, Light, Shutter