Warning: Wikipedia contains spoilers
In the first movie, the family's 5 year-old daughter, "Carol Anne," is taken through a television set by a group of ghosts and held hostage. A spiritual healer and a ghost expert are eventually brought in, allowing her mother to also pass through the TV to the "other world" to save her. The two sequels (1986 and 1988) followed a path of different ghosts stalking "Carol Anne" and her other family members too.
Some of the stars in the movie suffered unfortunate fate, for which the movie series has been dubbed as having a Poltergeist Curse.
A TV series, Poltergeist, The Legacy, is a spin-off of this movie series.
Movie producers had planned to film more sequels, but those plans were dashed by O'Rourke's death at the age of 12.
See also: Poltergeist