What is the geographical feature known as Tigris?

Tigris is a major river that flows through Turkey, Syria, and Iraq. It is one of the two major rivers, along with the Euphrates, that define the region of Mesopotamia, also known as the "Land Between the Rivers". The Tigris River originates in the Taurus Mountains in eastern Turkey and flows southeast until it converges with the Euphrates in southern Iraq, where the two rivers merge and become the Shatt al-Arab River, which flows into the Persian Gulf.