What phenomenon describes heat transfer through fluids such as gases or liquids?

The correct choice is convection because it specifically refers to the process of heat transfer through fluids, which includes both gases and liquids. Convection occurs when warmer areas of a fluid rise due to being less dense, while cooler, denser areas sink. This movement creates a continuous circulation pattern that effectively transfers heat throughout the fluid.

In practical applications, such as in heating a room or cooking food in boiling water, convection plays a crucial role. For example, as the water at the bottom of a pot is heated, it becomes less dense and rises, while cooler water descends to take its place, creating a flow that distributes heat evenly throughout the pot.

Understanding convection is vital for third-class power engineers, as it directly impacts the efficiency of heating and cooling systems used in various mechanical and process applications.