y-Scaling in quasi-elastic electron scattering by nuclei

y-Scaling in quasi-elastic electron scattering from nuclei is discussed paying particular attention to the question of the definition of the scaling variable. By analysing recent experimental data on 12C, it is shown that the scaling function F(y) should be defined in terms of a new scaling variable y1 which takes explicitly into account the effects from finite nuclear masses and nuclear binding; in the asymptotic limit y1 goes over into the usual scaling variable y0 = Mω/q - q/2. Some open problems concerning y-scaling in 3He are also discussed