A wraith is an apparition of a person who is still alive, seen as an omen that the person is about to die. It is a Scottish word, first attested in English in 1513, and the etymology might be from an Old Norse vörðr (lit. "warden"), denoting a kind of spiritual being in Norse faith.
Its modern connotations have been strongly affected by the ringwraiths in J. R. R. Tolkien's novel The Lord of the Rings. Tolkien's wraiths were a form of undead creature. Unlike other undead, however, these wraiths need not have passed through death to become undead. Instead, Tolkien's Ringwraiths were corrupted by evil such that they became purely soulless and under the control of Sauron, a powerful necromancer.
In the Harry Potter book series, by J.K. Rowling, Dementors are wraith-like creatures that psychically feed off of human misery and, if they are allowed to do so, will devour a person's soul.
In Dungeons & Dragons, wraiths are insubstantial ghost-like undead that drain life from the living with their touch. Creatures slain by a wraith's life-draining later rise as wraiths themselves.
In the Legacy of Kain video game series, one of the main characters, Raziel, is a wraith. Another video game character, Noob Saibot of the Mortal Kombat series, is considered a wraith, his soul having been tainted when he died at the hands of Scorpion.
One form of a wraith is a ghost of someones emotion. It is said when a person dies with anger a wraith will be formed from the anger. One example of a wraith is a poltergeist.