2. Any appearance or aspect of an object of mental
apprehension or view; as, the problem has many phases.
3. (Astron.) A particular appearance or state in a regularly
recurring cycle of changes with respect to quantity of
illumination or form of enlightened disk; as, the phases
of the moon or planets. See Illust. under {Moon}.
4. (Physics) Any one point or portion in a recurring series
of changes, as in the changes of motion of one of the
particles constituting a wave or vibration; one portion of
a series of such changes, in distinction from a contrasted
portion, as the portion on one side of a position of
equilibrium, in contrast with that on the opposite side.