An Earthbound Spirit is a spirit that has not left the Earth, they have not crossed over to the other side just yet. These spirits are the cause for many ghost sightings, and haunted houses. Some of these spirits are not happy that they are stuck on earth still. There are different reasons why the Earthbound spirits are still on Earth.
Some spirits who have died suddenly and unexpected remain at the scene of where they passed away. Not realizing that they are deceased, or not wanting to believe it. These spirits try to connect with people that can see or hear spirits.
Some spirits remain on Earth because they are scared of what is on the other side, so they stay here out of fear of what comes next. They accept that they are deceased but choose to cross over to the other side.
Some Earthbound spirits cannot leave the Earth due to things they need to take care of. Unfinished business such as making sure there loved ones will be okay with them passing, maybe they have to make sure their belongings and finances are intact. After they finish their business then they can cross over.