The effect of the secondary vaporization of the liquid after it's been liquified from gas during the continuous decompression or cooling (or both).
The term is misnomer as it actually means vaporization which is opposite to Condensation.
The most popular practical example of Retrograde Condensation behaviour is low-density alkanes.
See also
Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase / Phase transition
[ Condensation ][ Vaporization ]