Fusion
The change of state from a solid to a liquid at the same temperature. The heat of fusion is the number of gram calories of heat necessary to change one gram of a substance from the solid to the liquid state. It is the opposite of freezing.
Temperature
The measure of molecular motion or the degree of heat of a substance. It is measured on an arbitrary scale from absolute zero, where the molecules theoretically stop moving. It is also the degree of hotness or coldness. In surface observations, it refers primarily to the free air or ambient temperature close to the surface of the earth.
Heat
A form of energy transferred between two systems by virtue of a difference in temperature. The first law of thermodynamics demonstrated that the heat absorbed by a system may be used by the system to do work or to raise its internal energy.
Calorie
In meteorology, it is the amount of heat required to raise the temperature of one (1) gram of water one (1) degree Celsius. It is a unit of heat energy.
Freezing Point / Freeze
The process of changing a liquid to a solid. The temperature at which a liquid solidifies under any given set of conditions. Pure water under atmospheric pressure freezes at 0°C or 32°F. It is the opposite of fusion. In oceanography, the freezing point of water is depressed with increasing salinity.