liquidus

https://doi.org/10.1351/goldbook.L03590
A line on a binary phase diagram (or surface on a ternary phase diagram) that indicates the temperature at which
solidification
begins on cooling or at which
melting
is completed 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 585 [Terms] [Paper]