The term "phase" is also used when comparing a periodic function F with a shifted version G of it. If the shift in t is expressed as a fraction of the period, and then scaled to an angle \varphi spanning a whole turn, one gets the phase shift, phase offset, or phase difference of G relative to F. If F is a "canonical" function for a class of signals, like \sin(t) is for all sinusoidal signals, then \varphi is called the initial phase of G.
