One distinct stage of a longer process, with its own character. Phases follow; they do not overlap.
Greek φάσις (phasis, an appearance), from φαίνειν (phainein, to show, cause to appear); first the visible stages of the moon, later any one stage of a longer process with its own distinct look.
One distinct stage of a longer process, carrying its own character, and following the one before it rather than overlapping it.