As a noun, it is a distinct stage in a process, development, or cycle. As a verb (usually “phase in/out”), it means to introduce or remove something gradually in stages.
From Greek “phasis” meaning “appearance,” used in astronomy for the visible stages of the moon. It later widened to mean any recognizable stage in a process.
We borrowed ‘phase’ from how the moon changes shape in the sky, then applied it to everything from projects to teenage moods. Saying “It’s just a phase” hints that many intense experiences are actually temporary stages.
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