"Paranormal Activity" is a prime example of the found-footage horror genre, which has become increasingly popular in recent years. The film tells the story of a young couple, Katie and Micah, who set up a series of cameras in their home to document the strange occurrences they have been experiencing. As the film progresses, the events become increasingly disturbing and terrifying. The found-footage style of the film adds to the sense of realism and immediacy, making the horror more intense and believable.