Ghost and poltergeists have some similarities between them, but they are not the same. The activity of a ghost-like nature is known as haunting, while the activity of a poltergeist nature is known as a disturbance. One of the factors that also set the differences between these two entities is their origins.
Ghost is generally recognized as dead men that their spirit refuses to leave the earth (the realm of the living). They usually appear in several different forms, such as complete bodies, foggy mists, and transparent entities. Poltergeists are generally known as forms of energy that a living person unknowingly controls.
Poltergeists are known to appear by influencing or moving a human. Meanwhile, ghosts do not need to influence anyone; they just appear. So, this can make a ghost to be seen, but you cannot see a poltergeist. Ghosts are entities that might not necessarily be dangerous, but poltergeists are known to be generally dangerous.