The Day of German Unity (German: Tag der Deutschen Einheit) is the national day of Germany, celebrated on 3 October. It commemorates the anniversary of German reunification in 1990 when the goal of a united Germany, that originated in the middle of the 19th century, was fulfilled again. Therefore, the name addresses neither the re-union nor the union, but the unity of Germany.
An alternative choice to commemorate the reunification could have been the day the Berlin Wall came down: 9 November 1989, which coincided with the anniversary of the proclamation of the German Republic in 1918, and the defeat of Hitler’s first coup in 1923. However, 9 November was also the anniversary of the first large-scale Nazi-led program against Jews 1938, so the day was considered inappropriate as a national holiday.
This image, Berlin, deutsche Vereinigung, vor dem Reichstag, depicts the flag of unity raised at midnight 3 October 1990 in front of the Reichstag.
Attribution: Bundersarchiv, Bild 183-1990-1003-400/Grimm, Peer/CC-BY-SA 3.0