Illustrated Glossary of Organic Chemistry

Melting point (mp): The temperature (or more commonly temperature range) at which a substance undergoes a solid to liquid phase change (i.e., it melts) without an increase in temperature. Alternately, the temperature at which a substance exists in equilibrium between its solid and liquid phases. Used to characterize a compound, or a judge of purity.

Ice (mp 0 oC) keeps a drink at 0 oC while the ice
Laboratory apparatus for measuring melting point.
melts because melting ice absorbs energy from its

surroundings, but without a rise in the ice's temperature.