The concept of turbulent burning velocity arises from an analogy with that of the laminar burning velocity. Experimental measurement or theoretical computation of the latter must take account of the effects of flame stretch. This is also necessary for turbulent flames, and when flame propagation originates at a point source, there is a temporal development of the turbulence acting on the flame and also of the thickness of the flame brush. Under these conditions, while the turbulent burning velocity is a measure of the propagation rate of the front relative to unburnt mixture, it cannot be a direct measure of the mass rate of burning.