Question: what is the phase difference between two waves?
Answer: The phase difference of two waves is the horizontal distance a similar part of one wave leads or lags the other wave. Phase difference is measured in fractions of a wavelength, degrees or radians. In the diagram (above), the phase difference is ¼ λ. This translates to 90o ( ¼ of 360o ) or π/2 ( ¼ of 2π ).