Ruthenia is an exonym, originally used in Medieval Latin, as one of several terms for Rus'. Originally, the term Rus' land referred to a triangular area, which mainly corresponds to the tribe of Polans in Dnieper Ukraine. Ruthenia was used to refer to the East Slavic and Eastern Orthodox people of the Grand Duchy of Lithuania and the Kingdom of Poland, and later the Polish-Lithuanian Commonwealth and Austria-Hungary, mainly to Ukrainians and sometimes Belarusians, corresponding to the territories of modern Belarus, Ukraine, Eastern Poland and some of western Russia.
Historically, in a broader sense, the term was used to refer to all the territories under Kievan dominion (mostly East Slavs).
The Kingdom of Galicia and Lodomeria (1772–1918), corresponding to parts of Western Ukraine, was referred to as Ruthenia and its people as Ruthenians. As a result of a Ukrainian national identity gradually dominating over much of present-day Ukraine in the 19th and 20th centuries, the endonym Rusyn is now mostly used among a minority of peoples on the territory of the Carpathian Mountains, including Carpathian Ruthenia.