The Kalahari Desert is a semi-desert, which receives over 249 millimeters of rainfall (9.8 inches) in some areas. The desert derives its name from the Tswana word Kalagare meaning “a waterless place.” It covers approximately 900,000 square kilometers (347,500 square miles) and spans three countries namely, Namibia, South Africa, and Botswana, with the latter taking the lion’s share. Central Kalahari Game Reserve—the largest in the world—as well as Kgalagadi Transfrontier Park and Khutse Game Reserve are some of several conservation areas in the Kalahari Desert. It is sweltering in summer and very cold in winter, with temperatures hovering around 40°C and 0°C respectively. Most rivers that flow through the desert dry up except River Okavango, which is the only permanent river. Although the conditions are challenging, six significant tribes live in the Kalahari desert: Sun Bushmen, the Kung people, Namaqua, Griqua people and Khios people. The Sun Bushmen is one of the oldest cultures in the world; researchers allege that they have lived in the Kalahari desert for almost 20,000 years. The eland (Taurotragus Oryx), the largest antelope in Africa, lives in the Kalahari desert. Other animals include the gemsbok, leopards, lions, cheetahs, and caracals.