Physical Chem. a generalization in the study of equilibriums between two or more phases of a system, stating that the number of degrees of freedom is equal to the number of components minus the number of phases plus the constant 2, or F = C − P + 2
See phase rule in American Heritage Dictionary 4
noun Physics
A rule stating that the number of degrees of freedom in a material system at equilibrium is equal to the number of components minus the number of phases plus the constant 2. For example, the system of water vapor, liquid water, and solid ice has zero degrees of freedom because the three phases of vapor, liquid, and solid coexist in the one component, water.