As the moon orbits the Earth, its shape seems to change.  This is because the sun's light hits a different part of the moon as it moves around the Earth.  These changing shapes are called phases.  The phases of the moon are new, crescent, quarter, gibbous, and full.  A new moon is completely dark.  The moon is waxing if the light part of the moon is growing larger.   The moon is waning if the light part of the moon is getting smaller.  A full moon occurs when the entire moon is bright from the sun's light.  The moon completes its phases once every month.