Polish is a western Slavic language. Slavic is generally subdivided as Western, Eastern, and Southern.
Eastern and Western are contiguous, while Southern is on the other side of a corridor between Western Europe and the Black Sea German (Austria,) Magyar (Hungary,) and Romanian, which is Latin (Roman.)
Slavic is part of the Balto-Slavic branch of the Indo-European language family. Baltic lives on only in Latvian and Lithuanian.
Slavic is dominant in all of Eastern Europe except in the Baltic states, the corridor mentioned above, and in Estonia, whose language is (like Magyar) Finno-Ugric [and is thus not even Indo-European.]