Penumbra
Penumbra explained in an easy to understand way:
Imagine you're in a crowded room trying to listen to your favorite song playing softly in the background. Just like how the chatter of people can drown out the music, leaving you with only bits and pieces of the melody, the penumbra is a region where light only partially reaches, creating a lighter shadow around the darkest part. In this way, the people in the room are like the light source, the music is the main shadow, and the overlapping sounds are the penumbra, a space where the clarity of the song is compromised, just as the light is partially blocked in the penumbra.
Practice Version
Penumbra: A region of lighter shadow around the darkest part of a shadow. Penumbra. The penumbra is the partially shaded outer region of a shadow cast by an object, like during a solar eclipse.