Shadow People, what are they?
We don’t really know, however there are several theories.
One theory is shadow people are another way for ghosts to manifest. It takes less energy to reveal itself as a shadow then it does as an apparition. Most reports say that they appear as dark forms, silhouettes, seen with in the peripheral vision. Their movement can be swift especially if they realize they have been seen. They are mostly seen at night, however they can be seen in the day time hiding in the shadows.
Other theories are the imagination, demons, time travelers, interdimensional beings.
The imagination, illusions, our eyes are playing tricks on us, or real shadows caused by passing vehicle headlights. Demons, the dark shade of these beings led’s us to speculation. Time travelers, people from the future visiting us in the past. Interdimensional beings, some theorize that there are parallel dimensions and sometimes these dimensions cross into our world. Possibly allowing us a glimpse into another dimension, and the people who live in them.