Kush was the name of an early kingdom in northern Sudan and first appears in Egyptian texts about 2000 BC. The Egyptians, who were afraid of the growing power of Kush, habitually tied the name to an adjective meaning "vile" or "bad." The earliest capital of Kush was apparently located at the site of modern Kerma, Sudan, about 420 miles (700 km) upstream (south) from Aswan. Originally designating only Upper Nubia (i.e. northern Sudan), the term "Kush/Cush" (also "Kas, Kos") was eventually more freely interpreted to mean all of Nubia south of Aswan. This name was used not only by the Nubians themselves, but also by the Egyptians and the rest of the ancient world (prior to the Greeks). "Kush" or "Cush" is the name of Nubia used in the Old Testament. It was also the native name of the later ancient Nubian kingdom, which was centered first at Napata and then at Mero‘.
Source: http://www.nubianet.org

Source: http://www.touregypt.net