What is the difference between poltergeists and traditional ghosts?

Many people usually think that traditional ghosts and poltergeists are the same. In some cases, these types of ghosts could be the same. However, traditional ghosts are visible in many cases. On the other hand, poltergeists may not be visible. They may make their presence feel by slamming doors and throwing objects. So, what is the difference between poltergeists and traditional ghosts?