The point, with coordinates critical solution temperatures and critical composition, on a temperature-composition phase diagram at which the distinction between co-existent phases vanishes. In solid-solid, solid-liquid and liquid-liquid systems both upper and lower critical solution temperatures and corresponding critical solution compositions can occur. Synonymous with consolute point.
Source:
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 580 (https://doi.org/10.1351/pac199466030577)