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Phase
The phase of a periodic phenomenon at time t is its relative position to the period since the beginning of a new cycle.
Explanation
The phase of a 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 denoted Φ (t) and 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 2π as the variable t completes a full period.