Wraiths are a variant of ghost found in various myths, religions and assorted /tg/ media. The general difference is that whilst ghosts may be pitiable, wraiths tend to be actively malevolent, or at least so homicidally insane that you really can't spare the time to pity them before they suck out your life with a touch.
In Dungeons & Dragons it developed from the "Nazgul" in those halcyon days before came The Lawyers. Over the late 1970s they were split out: the Wraith for low-level play, and the Spectre carrying on the pterodactyl-riding Wraith-dominating tradition. Their stats were those of incorporeal Wights, with the same energy-drain.