Definition of phase

• (physical chemistry) a distinct state of matter in a system; matter that is identical in chemical composition and physical state and separated from other material by the phase boundary; "the reaction occurs in the liquid phase of the system"
• any distinct time period in a sequence of events; "we are in a transitional stage in which many former ideas must be revised or rejected"
• a particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle