In physics and mathematics, the phase (symbol φ or ϕ) of a wave or other periodic function F of some real variable t (such as time) is an angle -like quantity representing the fraction of the cycle covered up to t . It is expressed in such a scale that it varies by one full turn as the variable t goes through each period (and F ( t ) goes through each complete cycle). It may be measured in any angular unit such as degrees or radians, thus increasing by 360° or 2 π π as the variable t completes a full period.