What type of heat transfer occurs between two bodies at different temperatures?

The concept of heat transfer involves the movement of thermal energy from a region of higher temperature to a region of lower temperature. This process occurs primarily through different mechanisms, namely conduction, convection, and radiation.

While "Heat Transfer" is a general term that encompasses all these methods, when distinguishing the types of heat transfer that specifically occur between two bodies, we typically refer to conduction and convection.

Conduction is the direct transfer of heat through a material as particles collide with one another, which is significant in solids. Convection, on the other hand, involves the movement of fluid (liquid or gas) where warmer, less dense areas rise and cooler, denser areas sink, facilitating heat transfer through the bulk movement of the fluid.

While thermal expansion refers to the increase in volume of a substance due to an increase in temperature, it is not a type of heat transfer but rather a result of it.

In this question, recognizing the broad nature of the answer "Heat Transfer" helps to understand that it correctly describes the phenomenon of energy transfer due to temperature differences without specifying the method by which the transfer occurs.