Laminar flame speed is an intrinsic characteristic of premixed combustible mixtures.
[1] It is the speed at which an un-stretched laminar flame will propagate through a quiescent mixture of unburned reactants.
According to the thermal flame theory of Ernest-François Mallard and Le Chatelier, the un-stretched laminar flame speed is dependent on only three properties of a chemical mixture: the thermal diffusivity of the mixture, the reaction rate of the mixture and the temperature through the flame zone:
Turbulent flame speed is a function of the aforementioned parameters, but also heavily depends on the flow field.
As a result, the flame front of a turbulent flame will propagate at a speed that is not only a function of the mixture's chemical and transport properties but also properties of the flow and turbulence.