thermal diffusivity – A measure of how quickly a material transfers heat across a temperature difference. High thermal diffusivity can minimize the development of thermal gradients by allowing a part or parts to reach a uniform temperature quickly.
Material properties and thermal properties in particular tend to vary with temperature. Thermal diffusivity tends to vary inversely with temperature.
On Practical Precision, thermal diffusivity is represented by the symbol D.
In other references, α, a, κ, and K may be used.
D = thermal conductivity / (density x specific heat capacity) = k / (ρ x Cp)
Thermal diffusivity on Wikipedia