The lever rule is used to
The lever rule is used to calculate the relative concentration of two of these. Degrees of freedom for a system equal the number of components, minus the number of these, plus two, according to a rule named for Gibbs. There are two of them along the liquidus curve. At a given concentration, the dew point is the highest temperature at which two of these can coexist in a system.  The latent heat is the enthalpy associated with a transition between them. At the triple point, three of them exist. Diagrams depicting them usually plot pressure against temperature and are divided into regions. For 10 points, name these things which include solids, liquids, and gases.
The lever rule is used to calculate the relative concentration of two of these.
phases of matter [prompt on "states" of matter]