critical temperature

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The temperature above which a gas cannot be liquefied, regardless of the pressure applied.
• noun The temperature at which a material becomes a superconductor.
• noun The temperature at which a property of a material, such as its magnetism, changes.

from the GNU version of the Collaborative International Dictionary of English.

• (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The temperature at the critical point of a substance