Meaning

noun any distinct time period in a sequence of events

noun (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

noun a particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle

originFrom New Latin phasis, from Ancient Greek φάσις (phásis, “an appearance”), from φαίνω (phaínō, “to cause to appear”); compare phantasm and see face.

Etymology from Wiktionary, CC BY-SA 3.0