#Rear Curtain Sync
Rear Curtain Sync is a flash sync mode. The shutter opens and closes for a length of time determined by the shutter speed that has been set. Rear Curtain Sync is when the flash fires at the end of the exposure, or at the rear curtain. Picture a person walking in a dimly lit scene (so that a long exposure can be used) from camera left to camera right. If they start walking at the left of the frame and the camera is fired in Rear Curtain Sync mode, their motion trail will be behind them and they will be frozen somewhere mid-frame where they had walked to at the end of the exposure.