A phase is one of the different apparent shapes of the moon as seen from Earth. Come on. I'll tell you more when we get home.
Why do we see different moon phases?
As the moon revolves around Earth, the angle of light from the sun that's reflected is changing. The phase you see depends on how much of the sunlit of the moon faces Earth.
There are 8 phases. In order, there's new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, waning crescent, and then back to new moon
These are the waxing and waning crescents. Waxing means to grow and waning is to shrink. The moon gets larger and smaller from right to left. The one on the left is waning and the one to the right is waxing.
These are the waxing and waning gibbous. A gibbous is more than a semicircle, but less than a full circle. Third quarters are semicircles. Just remember, during a full moon, you're seeing 50% of the moon.