It is an eclipse during which the moon becomes darker.
How It Works
First, the moon enters the Earth's umbra, which is the dark shadow behind Earth.
Second, the moon enters the Earth's penumbra, which is above the umbra and is slightly lighter than it.
Types of Lunar Eclipse
When the moon is completely dark, it is called a full lunar eclipse.
When the moon is partially dark, it is called a partial lunar eclipse.