1. An equation that relates the vertical turbulent flux of a quantity to the shape or slope of the vertical profile of the mean value of that quantity, usually applied in the surface layer of the atmospheric boundary layer. For example, in the surface layer the wind speed increases approximately logarithmically with height, at a rate that depends on the friction velocity u* and the Obukhov length L. Because both these last two variables depend on surface fluxes, it is possible to find these fluxes from measurements of the mean wind profile, a technique that can be easier and less costly than measuring the fluxes directly. 2. Same as universal functions.