Technically, the moon doesn't "change" every night. The shape APPEARS to change. These are the phases of the moon or "cycle" of the moon if you prefer to call it.
When the moon appears to be getting bigger (moon phases from New to Full) it is known as waxing. When it is getting smaller (moon phases from Full to New) it is known as waning. Waxing means increasing. Waning means decreasing.
