Third Reich (German: Drittes Reich), Nazi term for Germany and its regime during the period of Nazi reign, from 1933 to 1945. The German word reich means kingdom or realm, and is used in a fashion similar to the word "empire."
The "Third Reich" term alludes to two different series of three. The first series is that of the three German empires: the Holy Roman Empire of the German People, which formally lasted until 1806, was considered the First Reich; the German Empire, which lasted from 1871 to 1918, was the Second Reich; while the Third Reich was the empire that the Nazis aspired to set up. The second series is a "spiritual" one that comes from the ideas of a twelfth century Christian mystic. He envisioned the history of man as a series of three thousand-year kingdoms: the "kingdom of the Father," the "kingdom of the Son," and the "kingdom of the Holy Spirit." This third kingdom (which the Nazis translated as the "Third Reich") was supposed to be actualized in the perfect world of the end of days, and as the Nazis came to power in the last century of the millenium, Hitler predicted that the Nazis' "Third Reich" would continue on for a thousand years.