A general term used to describe a transition in which the first and second derivatives
of the molar
Gibbs energy or molar
Helmholtz energy (or
chemical potential) with respect to temperature and pressure are continuous, but derivatives of some
higher order are discontinuous at the transition point. Synonymous with smooth transition.
Source:
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
1994))
on page 583