The Russian exclave located between Poland and Lithuania is Kaliningrad. More precisely, Kaliningrad is the principal city of Kaliningrad Oblast, a Russian semi-exclave on the Baltic Sea, separated from Russia's mainland by other countries.
The region was historically the northern part of East Prussia, and its main city was known as Königsberg until 1946. After World War II, the Soviet Union annexed the territory, expelled much of its German population, and renamed the city Kaliningrad after Soviet politician Mikhail Kalinin. When Lithuania and other Soviet republics became independent in 1990–91, the region became geographically detached from the rest of Russia.
Kaliningrad is sometimes confused with the Suwałki Gap, which is the narrow Polish–Lithuanian land corridor near the exclave, not the exclave itself. Crimea is also associated with Russia but is a peninsula on the Black Sea, while Brest is a city and region in Belarus. Kaliningrad's Baltic location gives Russia an important naval position, including the ice-free port of Baltiysk.