A dybbuk, according to Jewish folklore is the ghost of a dead person, usually a wicked or evil person, which is able to possess a living person. Once a dybbuk has completed the task that it set out to do, it is said to leave the body of the person that it possessed. A rabbi may also be able to force a dybbuk to leave the person's body. The word "dybbuk" is an abbreviation of the Hebrew dibbuk min ha-hizonim (evil spirit from outside) or dibbuk me-ru'ah ra'ah (clinging evil spirit).
Although demonic possession was referred to by earlier Jewish writers, who stated that those who fell victim to it were usually Jews who did not follow rituals correctly or who questioned their religion, there are no references to possession by ghostly dybbuks before the 16th century.
The idea of dybbuks was introduced to a wider audience by the 1914 Yiddish play The Dybbuk; or Between Two Worlds (Der Dibuk oder Tsuishin Tsvey Veltn) by the Russian playwright Shlyome Zanvl Rappaport, who wrote under the name of S. Ansky. In the play, a scholar named Hannan falls in love with a woman named Leah'le whom he feels he is predestined to marry. When Hannan finds out that Leah'le is to marry somebody else, he dies. Hannan's dybbuk takes possession of Leah'le before her wedding. The dybbuk leaves Leah'le's body when it fulfills its purpose, getting Leah'le's father to admit that he had promised that Hannan and Leah'le would marry and then broke his word. Hannan's ghost appears to leah'le at the end of the play. She decides to stay with him, which suggests that she chooses to follow him in death.
A recent addition to the dybbuk myth is the idea that a dybbuk can be trapped in a wooden box called a dybbuk box. A dybbuk may, however, be able to escape from the box and bad luck is likely to follow anyone who owns a dybbuk box.
A dybbuk should not be confused with an inbur, another type of ghost in Jewish folklore. An inbur is said to be the ghost of a righteous person which can temporarily possess a living person, if the living person requests it to do so.