Before revision: The square root of the product of thermal conductivity, density, and specific heat capacity is called thermal effusivity, and tells how much heat energy the body absorbs or releases in a certain amount of time per unit area when its surface is at a certain temperature.
After revision: The square root of the product of thermal conductivity, density, and specific heat capacity is called thermal effusivity, and determines how much heat energy the body absorbs or releases in a certain amount of time per unit area when its surface is at a certain temperature.