Individuals who have not succumbed to a histiminilitic virus in the Land of Light -- evidently bearing some natural immunity. Before SG-1's arrival on the planet the Untouched had long believed that their loved ones lost to the virus, the Touched, were effectively dead -- as there was nothing they knew to be done for them.
The Untouched isolated the Touched outside the Land of Light, in the dark regions surrounding the Stargate, to live free from their barbaric, Neanderthal-like behavior.
SG-1's arrival to the world brought antihistamine vaccines that cured the population, allowing the Touched to return to their families in the Land of Light.
The Broca Divide - SG-1 arrives on a world where there are two distinct groups of people: the Untouched, and the Touched.