Turkestan, tur kih STAN, also spelled Turkistan, is a vast region in Asia. It has no definite boundaries. Turkestan stretches from Siberia on the north to Iran, Pakistan, India, and Tibet on the south. The Mongolian Desert lies to the east, and the Caspian Sea to the west. The name Turkestan refers to the Turkic-speaking tribes that have lived in this region since as early as the A.D. 500's.