The Collaborative International Dictionary of English v.0.48:

critical temperature \crit"ic*al tem"per*a*ture\ (Physics),
   A certain temperature, different for different gases, but
   always the same for each gas, regarded as the temperature
   above which no amount of pressure can produce condensation to
   a liquid; the temperature above which a gas cannot be
   liquified.
   [1913 Webster]