The term "Nubia" is of relatively recent coinage, and refers to a region that never called itself by that name. The name derives etymologically from the names of the indigenous languages spoken in the region: collectively, the Nubian language family.
The term Nubia today is used differently in different contexts. As a cultural and geographical term, it usually designates the region extending southward from the First Cataract of the Nile, in southern Egypt, as far as the confluence of the Blue and White Niles, in central Sudan. As an ethnonym it refers to a much more restricted area, in the far south of Egypt and the far north of the Sudan, that is still inhabited by Nubian speakers who are today entirely surrounded by Arabic-speakers. They are only a small minority of the population in both Egypt and the Sudan.
There never was a political entity called Nubia. The region was known to ancient Egyptians (and in the Bible) as the land of Kush, and to Greeks and Romans as Aethiopia. The indigenous empire which arose in the last millennium BC called itself Kush, while the Christian kingdoms that succeeded it had the separate names of Nobadia, Makouria, and Alodia. Medieval Arab writers usually referred to them by their individual names, but sometimes designated them collectively as Beled-es-Sudan, the Land of the Blacks. Since the beginning of the 20th century the region in question has been divided politically between the nation-states of Egypt and the Sudan, but does not form a major part of either one.
As employed throughout this website, Medieval Nubia will designate the region extending from the First Nile Cataract to some point not far south of the junction of the Niles -- the site of modern Khartoum. Although the southern half of this region is today occupied by Arabic-speakers, evidence suggests that in medieval times it was occupied entirely by Nubian speakers. Though never unified politically, there was a community of culture and religion, and quite possibly of language, throughout the region, setting it clearly apart from Muslim Egypt to the north, from the pagan Sudan to the south, and from the pastoral nomad regions to the east and west. It was the scene of one of Africa's truly distinctive indigenous civilizations, a fact which is only now beginning to be fully appreciated.
(Article contributed by William Y. Adams.)