ELI5: Explain Like I'm 5

Lunar month

A lunar month is how long it takes for the Moon to go all the way around the Earth. It takes about 28 days for the Moon to make one full trip around the Earth. Each day, the Moon looks a little bit different in the night sky. Some nights there's a full Moon, some nights there's no Moon at all, and some nights you can see just a small part of the Moon in the sky!