1. (Physics) A space entirely devoid of matter (called also,
   by way of distinction, absolute vacuum); hence, in a more
   general sense, a space, as the interior of a closed
   vessel, which has been exhausted to a high or the highest
   degree by an air pump or other artificial means; as, water
   boils at a reduced temperature in a vacuum.




2. The condition of rarefaction, or reduction of pressure
   below that of the atmosphere, in a vessel, as the
   condenser of a steam engine, which is nearly exhausted of
   air or steam, etc.; as, a vacuum of 26 inches of mercury,
   or 13 pounds per square inch.