What is the process by which heated gas or liquid moves between two surfaces at different temperatures?

The process you are referring to is convection, which involves the movement of heated gas or liquid between surfaces that are at different temperatures. In convection, warmer, less dense fluids rise while cooler, denser fluids sink, creating a continuous circulation pattern. This transfer of heat occurs in fluids (liquids and gases), where the heated fluid carries energy away from the source of heat and transfers it to cooler areas.

This is distinctly different from other forms of heat transfer. Conduction refers to heat transfer through direct contact between solid surfaces without any movement of the material as a whole. Radiation involves the transfer of heat through electromagnetic waves, allowing heat to move through a vacuum or without a medium. Insulation, on the other hand, is a method to reduce heat transfer rather than a process of transferring heat itself. Therefore, the characteristics and mechanisms of convection make it the correct answer for this particular question.