What information does a pressure-temperature (P-T) phase diagram provide?

A P-T diagram shows phase stability regions (solid, liquid, gas) as functions of pressure and temperature. Key features: vapor pressure curve (liquid-gas boundary ending at critical point), sublimation curve (solid-gas boundary), fusion curve (solid-liquid boundary), triple point (all three phases coexist), and critical point (above which liquid and gas are indistinguishable). It helps determine phase at given conditions, boiling/condensation points at various pressures, and whether a substance can exist as liquid at given conditions.