https://doi.org/10.1351/goldbook.15346
Graphical representation, by use of points, lines, and surfaces, of the phases present at chemical equilibrium in unary, binary, ternary, and higher-order systems containing two or more phases.
Note: Phase diagrams may employ any pairs of the variables temperature, pressure, and compositions of various phases. Thus, temperature-composition and pressure-composition phase diagrams are possible, as well as diagrams showing only compositions under isothermal or isobaric conditions.
See also: isopleths