The melting point of a substance is the temperature at which it changes from a solid to a liquid. It is a physical property often used to identify compounds and check purity.
Sodium chloride (NaCl) has a very high melting point of 801 deg C in aqueous solution. This is because of the nature of ionic bonding, which is one of the most attractive forces between molecules.
A solid compound’s melting point depends on the strength of those attractive forces, and also the structure and the nature of its intermolecular bonds. For example, sugar (Sucrose) crystals are made of intermolecular hydrogen bonds and have a very low melting point of 186 oC.
The melting point of a chemical is the highest possible temperature that it can melt without breaking its bonds. This makes it the most difficult chemical to determine, but it can also be used to differentiate a substance from other compounds that may have similar melting points.