1. Of a periodic, varying phenomenon, e.g., an electrical signal or electromagnetic wave, any distinguishable instantaneous state of the phenomenon, referred to a fixed reference or another periodic varying phenomenon.
Notes
1: Phase, i.e., phase time (frequently abbreviated simply to "phase" in colloquial usage), can be specified or expressed by time of occurrence relative to a specified reference.
2: The phase of a periodic phenomenon can also be expressed or specified by angular measure, with one period usually encompassing 360° (2Π radians).
3. That period of time during which a specified function occurs in a sequential list of functions.
4. The relationship between a signal and its horizontal axis, also called zero-crossing point.