A value used in heat-transfer studies and calculations to compare heat losses by conduction from various shaped objects under various conditions. It is combined into a single number that is the function of the actual heat loss (Q), the temperature difference (ΔT) between the body and its surroundings, the size (d) and shape of the body, and the thermal conductivity(k) of the fluid surrounding the object, in the equation Nu = Qd/ΔTk.