shutter shock is the vibration-induced blurring of images as a result of various movements of the camera shutter prior to exposure which consists of two main components:
winding the mechanical shutter
firing the 1st curtain of the mechanical shutter
note that this is different to camera shake caused by the mirror moving up which is another big factor in blurred images (this is not present in mirrorless cameras and can be minimised by using mirror lock up and a self-timer to postpone the shot until the vibrations settle down)
shutter shock mainly causes blurring at shutter speeds of 1/4 sec to 1/125th sec
it is NOT helped by self-timers, mirror lockup, image stabiliser or using a tripod
it can be reduced substantially by using electronic first curtain shutter (EFCS) or silent full electronic shutter mode1)