It is a name for a specific sect of Gnostics, but also a category created by scholars to refer to a number of sects that are related to Valentinians. The Sethians as a group were known to Hippolytus who dedicated Book Five in his work, "The Refutation of All Hereseys", to denouncing them. (See Gaffney) Seth was a character of Gnosticism who represented a savior figure and third son of Adam, founder of the Gnostic race. Generally Sethian works include, "Pistis Sophia", "Allogenes", "The Gospel of Mary", "Sentences of Sextus", "Marsanes", "Gospel of The Egyptians", "The Apocalypse of Adam", "Origin of The World", "The Gospel of Thomas", "The Gospel of Philip", "The Three Steles of Seth", "Melchizidek", "The Apocryphon of John", "The Gospel of Judas", Trimorphic Protennoia", the un-named text in the Bruce Codex, and "Zostrianos". (Others) Some Sethian works suggest strong ties with Jewish Gnosticism, as well as Platonic thought, as well as Zoroasterism. (They maintained three principles; darkness below, light above, and spirit in-between, according to work attributed to Dr. Roy Blizzard, University of Texas. See also; "Sethian Gnosticism, A Literary History", Turner) see also; http://en.wikipedia.org/wiki/Sethian (* Indicates works from the Nag Hammadi Lib., with other works by the same name.)