a. Any airway in which vapid air flows from the workings to the upcast
shaft or fan. See also: intake
b. Any airway which carries the ventilating air from the face outby and
out of the mine. BS, 8
c. Any surface turned back from the face of a principal surface.
d. The rate of profit in a process of production per unit of cost.
Dictionary of Mining, Mineral, and Related Terms