Thermal convection is the type of heat propagation that occurs in fluids in general, due to the difference in density between the parts that form the system. For example, in the refrigerator, food is cooled in this way. As we know, warm air is less dense than cold air and this is why the freezer is at the top of the refrigerator.
In this way convection currents are formed: the warm air from the food rises to be cooled and the cold air descends cooling the food, keeping it well preserved. This also explains why the air conditioner is placed on top of the room.