Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Sublimation is an endothermic phase transition that occurs at temperatures and pressures below a substance's triple point in its phase diagram. The reverse process of sublimation is desublimation or deposition, in which a substance passes directly from a gas to a solid phase. Sublimation has also been used as a generic term to describe phase changes between solid and gas that avoid the liquid state without specifying the direction of the transition.