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Conduction refers specifically to the transfer of heat through direct contact between substances. When two materials with different temperatures are in contact, heat moves from the hotter material to the cooler one until thermal equilibrium is reached. This process occurs at the molecular level, where faster-moving (hotter) molecules collide with slower-moving (cooler) molecules, transferring energy in the form of heat.

The other options represent different modes of heat transfer. The first option involves convection, which is the transfer of heat through the movement of fluids. The second involves radiation, where energy is transferred through electromagnetic waves and does not require a medium. Lastly, heat transfer through a vacuum is also a form of radiation and does not rely on direct contact between substances. Thus, the concept of conduction is distinct and specifically applies to situations where substances are in direct contact.