Reich is the German word for "realm" or "empire", cognate with Scandinavianrike and Dutchrijk. It is the word traditionally used for sovereign entities, including Germany. For instance, any country with a King or Queen as head of state, such as Britain, is a Königreich (kingdom). It is still used as a suffix in certain country names, for instance Frankreich (France).
The Nazis, eager to present their rule as a continuation of a Germanic past, used the term Das Dritte Reich (“The Third Reich”), counting the Holy Roman Empire as the first and the 1871 Empire as the second. They also used the political slogan"Ein Volk, ein Reich, ein Führer" ("One people, one country, one leader").
A number of words used by the Nazis which earlier were neutral have later taken on a negative connotation in German (e.g. Führer or Heil); the word "Reich" is usually not one of them, although in certain contexts it does carry a connotation of German imperialism. The word is still used with the Reichstag building, which again, since 1999, houses the German federal parliament (today called Bundestag), and for the old Reichstag institution.
The Lord's Prayer (first translated into Germanic language by Bishop Ulfilas) uses the words in the German version Dein Reich komme for "thy kingdom come".