a port on the Beta that can be used as flash sync connector (x-type):
X (xenon) sync is a mode designed for use with electronic flash. In this mode, the timing of the contacts coincides exactly with the full opening of the shutter, since xenon flashes respond almost instantly.
from:
http://en.wikipedia.org/wiki/Flash_synchronization#M.2C_F.2C_FP.2C_X_and_HSS_sync