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Conduction is the process by which heat energy is transferred through a material without any overall movement of the material itself. It occurs when molecules within a material come into direct contact with one another, allowing kinetic energy from higher-energy (hotter) molecules to be transferred to adjacent lower-energy (cooler) molecules. This direct transfer of energy through molecular collisions is what characterizes conduction.

The other statements address different modes of heat transfer. While heat can move through liquids and gas layers, these processes are primarily associated with convection, where bulk movement of the material carries energy. Radiation, indicated in one of the options, refers to heat transfer through electromagnetic waves and does not require a medium, distinguishing it from conduction. Thus, the focus on direct molecular contact is what makes the correct answer the best descriptor of conduction.