solidus

https://doi.org/10.1351/goldbook.S05738
A line on a binary phase diagram (or a surface on a ternary phase diagram) that indicates the temperature at which a system becomes completely solid on cooling or at which @[email protected] begins on heating under equilibrium conditions.
Source:
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 590 [Terms] [Paper]