Trans-Olza, also known as Trans-Olza Silesia, is a territory in the Czech Republic, which was disputed between Poland and Czechoslovakia during the Interwar Period. Its name comes from the Olza River.

The First Czechoslovak Republic, often colloquially referred to as the First Republic, was the first Czechoslovak state that existed from 1918 to 1938, a union of ethnic Czechs and Slovaks. The country was commonly called Czechoslovakia, a compound of Czech and Slovak; which gradually became the most widely used name for its successor states. It was composed of former territories of Austria-Hungary, inheriting different systems of administration from the formerly Austrian and Hungarian territories.