Burning velocity is the speed at which a flame front propagates relative to the unburned gas. This differs from flame speed. The laminar burning velocity (SL) is the speed at which a laminar (planar) combustion wave propagates relative to the unburned gas mixture ahead of it. The fundamental burning velocity (Su) is similar, but generally not identical to, the observed laminar burning velocity.
This is because Su is a characteristic parameter referring to standardized unburned gas conditions (normally 760 mm Hg and 25°C), and which has been corrected for nonidealities in the measurement. The turbulent burning velocity (St) exceeds the burning velocity measured under laminar conditions to a degree depending on the scale and intensity of turbulence in the unburned gas.