I am having a bit of difficulty understanding the statement of Fourier's law of heat conduction.
As mentioned in Georg Joos , Theoretical Physics
The quantity of heat passing per second through unit area of a surface normal to the direction of flow, is proportional to the negative of the temperature gradient.
My conceptual difficulty is with the phrase 'direction of flow'. Now heat is just energy, a scalar and this phrase somehow seems to imply that this energy has some kind of velocity, which seems weird.
Can someone explain how this should be interpreted.