What is "morgause"

Morgause is a character in later Arthurian traditions, appearing in Thomas Malory's 15th-century text Le Morte d'Arthur as the mother of Gawain and Mordred, both key players in the story of King Arthur and his downfall. Mordred is the offspring of Arthur's inadvertent incest with Morgause, the king's estranged half-sister. She is also a sister of Morgan le Fay and the wife of King Lot of Orkney, as well as the mother of Gareth, Agravain, and Gaheris.