supercooling and sublimation
sublimation is the direct passage between the solid state to the gaseous state, without spending time in the liquid state. This is the normal method by which dry ice dissipates, and is common in many situations involving water.
A much earlier message from someone stated that energy input is needed to convert water to ice. In fact, the opposite is true - you remove energy to convert water to ice. In the reverse case, there is a parameter called the energy of fusion, easily demonstrated by applying heat to a mixture of water and ice. The temp remains right at the freezing point, no matter how much heat you apply,, until the ice is all melted, at which point the temp begins to rise.
wikipedia should have more appropriate definitions...