Terek (tyĕˈrĭk) [key], river, c.370 mi (600 km) long, in Russia and Georgia, rising in the Caucasus, in Georgia, in glaciers W of Mt. Kazbek. It flows N through the Daryal gorge past Vladikavkaz, then E past Grozny and NE into the Caspian Sea. Below Kizlyar it forms a swampy delta c.60 mi (100 km) wide. In its lower course the Terek is used for irrigation. The upper valley is paralleled by the Georgian Military Road.