Wiktionary
phase diagram
n. 1 (context physics chemistry English) A graph, with axes representing temperature and pressure, showing the equilibrium conditions for a given substance to be a solid, liquid or gas. 2 a similar diagram for a binary mixture of substances, with axes representing composition and temperature.
Wikipedia
Phase diagram
For the use of this term in mathematics and physics, see phase space.
A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases occur and coexist at equilibrium.