ELI5: Explain Like I'm 5

Earth phase

Earth phase is the shape of the moon in our sky. It changes throughout the month in different shapes. The way the moon looks depends on how the sun is shining on it. The moon is round, but because the sun's light only hits part of it, it only looks like parts of it are lit up. That's why we can see different shapes of the moon in our sky, like a crescent, quarter, or gibbous.