What is defined as the transfer of heat by the movement of fluids or air?

The transfer of heat by the movement of fluids or air is known as convection. This process occurs when warmer fluid or air rises due to its lower density, while cooler fluid or air descends, creating a circulation pattern that facilitates heat transfer. In practical applications, such as heating and air conditioning systems, convection plays a crucial role in distributing thermal energy, ensuring that spaces maintain a desired temperature efficiently.

In contrast, conduction refers to heat transfer through direct contact between materials, where heat moves from the hotter object to the cooler one without any movement of the materials themselves. Concentration does not pertain to heat transfer processes but rather to a measure of how much of a substance is present in a given volume. Heat exchange is a broader term that could encompass various forms of heat transfer, including conduction, convection, and radiation, but it does not specifically denote the fluid or air movement aspect described in the question. Thus, convection is the most accurate term associated with the movement of fluids or air leading to heat transfer.