Wavelength of a light wave is the geometrical path or distance between two successive points, along its direction of propagation, having the same phase. This is dependent on the medium.
Frequency of a light wave is the number of times the magnetic field or the electric field at a point on the path of the wave, oscillates to maximum amplitude in one second. Frequency is independent of the medium in which the light wave is traveling.
Frequency can also be = speed of light/ wavelength