"Reich" roughly translates into "realm." The word itself was a common one to refer to Germany prior to 1945. The Weimar Republic still used the term Deutsches Reich to refer to itself and its instutions. The word itself was fairly innocuous in nature. But the numeric designation of first, second, and third was much more politicized than Deutsches Reich.

Although historians generally term the HRE the first Reich and Imperial Germany as the second, the term is a bit slippery. Although Germans often used "Reich" to refer to both these polities, the idea of a line of continuity (first, second, third) was much more hazy. The 1923 nationalist book Das Dritte Reich by Arthur Moeller van den Bruck popularized the term "Third Reich" and firmly set the definition of the HRE as the first and Imperial Germany as the second and prophesied that a third and final Reich would complete the work of the other two after a successful right-wing revolution. However, the roots of the term actually predated the Weimar Republic and featured in various nineteenth-century völkisch works of literature and philosophy. Van der Bruck's book was highly influential among nationalist circles in the Weimar Republic including the nascent NSDAP. After the NSDAP seizure of power in 1933, the official name of the German state was either the Deutsches Reich or the Großdeutsches Reich; the term Third Reich tended to be used unofficially. Hitler actually preferred to use Thousand-Year Reich over Third Reich because the latter implied his regime could be replaced.

The important lesson in all of this is that this process of numbered naming is highly politicized to create a false sense of historical continuity. The HRE had a long and storied history that gets obscured by terming it the First Reich; for Germans the Reich meant very different things in, say, 800, 1648, or 1806. Similarly, van den Bruck's numerical schema deliberately excludes two periods of German history, 1806-1871 and the Weimar Republic, and castigated them as antithetical to his conceptualization of the German polity's true nature.