What is penumbra definition?

The penumbra is the outer part of a shadow that is caused by the partial blocking of light. It is the region where the light is partially blocked and where there is a gradual decrease in its intensity. In astronomy, the penumbra refers to the outer edge of the shadow cast by a celestial body during an eclipse. The penumbra is the region where the eclipse is only partial and is surrounded by the more complete shadow known as the umbra. The term penumbra is also used in medicine to refer to the area surrounding a stroke-affected brain tissue, where the blood flow is reduced but not completely blocked.