What is "haratin"

Haratin (also transliterated Haratins, Harratins or Haratine, etc., singular Hartani) are oasis-dwellers in the Sahara, especially in southern Algeria, Morocco, Mauritania and Western Sahara, who make up a socially and ethnically distinct group of largely settled, non-nomadic workers, with relatively dark complexions, speaking either Berber or Arabic.