A Boulder Push (also called a Rock Push or bawi milgi) is a motion like that of pushing an imaginary boulder. The intent is to focus the practitioner's mind and control his or her breathing. The Boulder Push is used in the Sipjin form, for example.
The Boulder Push is performed from a Front Stance with one hand starting at the waist and the other at the side. Both hands are held palm-down, in an Arc Hand gesture, with the thumbs and fingers nearly touching. Both hands are pushed upward and outward diagonaly to about face-height. At the end, your eyes should be looking through the gap in the hands.