Noun
heat absorbed by a unit mass of a solid at its melting point in order to convert the solid into a liquid at the same temperature
Source: WordNetthe heat of fusion is equal to the heat of solidification Source: Internet
It is also noteworthy that helium's heat of fusion of only 0.021 kJ/mol is so weak of a bonding force that zero-point energy prevents helium from freezing unless it is under a pressure of at least 25 atmospheres. Source: Internet
If the substance is one of the monatomic gases, (which have little tendency to form molecular bonds) the heat of fusion is more modest, ranging from 0.021 to 2.3 kJ per mole. Source: Internet