A crescent moon is defined as the moon phase that is a few days after a new moon. A gibbous moon is the moon phase that is between the first quartet and the full moon. and Waxing is the phase of the moon when it is growing in size from new moon to full moon. • Waning is the shrinking phase of the moon when it is decreasing in size from full moon to new moon when it cannot be seen at all by us.