What is the fuzzy part of a shadow?

The fuzzy part of a shadow, often referred to as the penumbra, occurs when an object partially blocks a light source. This creates a gradient of light intensity at the edges of the shadow, resulting in a soft transition between the fully shaded area and the illuminated regions. The penumbra contrasts with the umbra, which is the darker central part of the shadow where the light source is completely blocked. This phenomenon is influenced by the size and distance of the light source relative to the object casting the shadow.