An area of Central Europe north of the Carpathian mountains. It stretches roughly from Cracow in the west to Bukovina in the east.
Galicia was a province of Poland from its earilest days until the first partition of Poland in 1772, when it was handed over to the Austrian Empire. Its principal city was Lviv (aka Lemberg). A sliver of territory between Cracow and Katowice was an independent "Free City of Cracow" until 1846, when the Austrians absorbed it.
In 1919, the Treaty of Versailles made Western Galicia part of a reconstituted Polish state. Exploiting the Russian Civil War of 1918-1920, Poland invaded Western Russia and took territories where Poles were not the dominant ethnic group, but which had been part of the medieval kingdom of Poland-Lithuania: Eastern Galicia and parts of what are now Ukraine, Belarus, and Lithuania.
When Adolf Hitler and Joseph Stalin divided Poland between them in 1939, permitting World War II to start, Galicia was permanently divided.
The Soviet Union kept most the half of Poland it took in the partition. When it broke up in 1991, Eastern Galicia became part of Ukraine.
Western Galicia is essentially the Polish voivodships of Malopolskie and Podkarpackie. Eastern Galicia now consists of the Ukrainian Oblasts of Lviv, Ternopil, and Ivano-Frankivsk.