What does the word 'critical point' signify in thermodynamics?
The critical temperature of a substance is the greatest temperature at which it may exist as a liquid without becoming a gaseous substance. The critical point between the liquid and vapour phases, for example, describes the conditions under which a liquid substance can coexist with its vapour. A given gas cannot be liquefied simply by applying pressure to it at a high enough temperature point (above the critical temperature).