end-port

from The Century Dictionary.

• noun In machinery: The opening at either end of the face of the valve-seat of a steam-engine, or the traverse of the valve thereon, through which steam is admitted alternately to the crank-end and to the head-end of the cylinder.
• noun In gas-engines, an opening through the wall of the cylinder which is uncovered by the travel of the piston just as it reaches the end of its stroke. Such end-ports release the exhaust gases at the end of the stroke, particularly in the two-phase cycle type of engine.