A shaded area on something such as a map is one that is coloured darker than the surrounding areas, so that it can be distinguished from them. (如地图上的某区域)颜色较深的
adjective [原级]荫蔽的;色彩较暗的
Here is a better picture. I claim that what will be going through C is this shaded parallelogram to the left of C. 这里有幅更好的图。我说经过 C 的是 C 左边的这个阴影平行四边形。