an extensive region of central Asia between Siberia in the north and Tibet, India, Afghanistan, and Iran in the south: formerly divided into West (Russian) Turkestan (also called Soviet Central Asia), comprising present-day Turkmenistan, Uzbekistan, Tajikistan, and Kyrgyzstan and the S part of Kazakhstan, and East (Chinese) Turkestan, approximating to the Xinjiang Uygur Autonomous Region of China