When someone says that they've seen a ghost, they usually are talking about a shadow person. The difference between a spirit and a shadow person is that the shadow person was never human. They can manifest by utilizing negative energy, which makes them ill-willed and usually angry. They can even cause people to feel dread and fear.
Since they're not human and manifest by using the energy of a home, they can appear in different shapes and manners. Depending on how they appear and what they do, you can determine what kind of shadow person you're dealing with.
Human Shaped
This is by far the most common shape of the shadow person that witnesses have seen. They've been described as missing facial features, pieces of clothing, hair, or outer features. Sometimes, they are transparent but have been described as “black static.” Shadow people are usually described as a male in appearance, although children and women have been described in different accounts.
The shadow people can move through walls and usually hang out in peoples' peripheral vision.
Black Mists/Dark Ectoplasm
Naturally, these types of experiences are usually much more negative than seeing a person-form. A lot of times, these are fast-moving and intelligent. The goal if this entity is to frighten people to harness more negative energy.
Other, More Rare Types
Some people have claimed to see animals, or shadows low to the ground that seem like they would be animals. There have also been accounts of "children" shadow people, or shadows that peer around corners or from behind furniture. These entities are shyer and prefer being in the darkness. Not all shadow entities are evil, especially the ones that seem to prefer to hide.