It is the transfer of Heat or Electricity through a substance, resulting from a difference in temperature between different parts of the substance or from a difference in electric potential. Heat may be conducted when the motions of energetic (hotter) molecules are passed on to nearby, less energetic (cooler) molecules, but a more effective method is the migration of energetic free electrons.

Conduction of electricity consists of the flow of charges. Metals are thus good conductors of both heat and electricity because they have a high free-electron density.