The Reichstag (German for "Imperial Diet") was the parliament of the Holy Roman Empire, and subsequently of the North German Confederation, and of Germany until 1945. The main chamber of the German parliament is now called Bundestag ("Federal Diet"), but the building in which it meets is still called "Reichstag" (see Reichstag (building)).
The term "Reichstag" is a compound of German Reich ("Empire") and Tag ("assembly"; does not mean "day" here, but is derived from the verb tagen "to assemble" (which in turn does mean to gather on an appointed day). The Latin term, a direct translation, was curia imperialis. (Still today, the parliaments on the various federal levels in Germany are called Bundestag, Landtag etc., and the parliament in Sweden is called Riksdag.)