Sulphured Molasses is molasses made from young sugar can and has sulfur dioxide added to it to keep the raw cane fresh until it is processed and to preserve the byproducts of the molasses that are produced from it.
Unsulphured Molasses is just molasses without those preservatives and without sulfur dioxide added to it.
When buying molasses it should say whether it's Unsulphured or Sulphured.