The original experimentalist (Michelson) gave perhaps the best lay mans description in terms of an analogy with a swimmer crossing a fast moving river. Long sto

The original experimentalist (Michelson) gave perhaps the best lay mans description in terms of an analogy with a swimmer crossing a fast moving river. Long story short, an interferometer detects the difference between two swimmers in their apparent distance swam (number of strokes they had to make), even though the physical distance traversed was the same for both. In this analogy the swimmers are individual photons of light and the "number of strokes" actually means the peaks / troughs of a given wave of light. Basically, a beam of light is split and then meets up again. If the length of the two paths are different, the peaks and troughs of the light wave will have drifted out of sync when they meet back up, and that will cause the interference pattern of the light wave interfering with itself to shift in proportion to the amount of drift. "Phase" is just the word scientists have settled on to describe this offset effect. Amplitude, wavelength and phase together give a complete description of any wave (light or otherwise). Hope that takes the mystery out of this "intrinsic physical property". Everything you wrote was accurate. I am merely expanding on the gaps.