History of Sudan
The modern Republic of Sudan was formed in 1956 and inherited its boundaries from Anglo-Egyptian Sudan, established in 1899. For times predating 1899, usage of the term "Sudan" for the territory of the Republic of Sudan was somewhat anachronistic, and may have referred to the more diffuse concept of the Sudan.
Sudan (region)
Historically, the name was understood to denote the western part of the Sahel region. It thus roughly encompassed the geographical belt between the Sahara and the coastal West Africa. In modern usage, the phrase "The Sudan" is also used in a separate context to refer specifically to the present-day country of Sudan, the western part of which forms part of the larger region, and from which South Sudan gained its independence in 2011.