This question may sound dumb, (it will to me, hopefully, in a day or two!), but does the term phase difference apply only for sinusoidal waves?
Wikipedia defines 'phase' as the following:
Phase in sinusoidal functions or in waves has two different, but closely related, meanings. One is the initial angle of a sinusoidal function at its origin and is sometimes called phase offset or phase difference. Another usage is the fraction of the wave cycle that has elapsed relative to the origin.
I'm confused about this specific part:
Another usage is the fraction of the wave cycle that has elapsed relative to the origin
Can this definition apply for any wave function, or just sinusoidal ones?