Frau was a German word for a woman. It could be used as a title in front of the name as in the case of Frau Tod and Frau Herz. (AUDIO: The Beast of Orlok, A Shard of Ice) It could also be used in front of a title. Ingrid Karnstein was referred to as Frau Doktor. (PROSE: White Darkness)
The term continued to be used after Earth's destruction, as in the case of Frau Clovis. (TV: New Earth)
The related term fraulein referred to younger women. The actor "Arab sheik" addressed the "vamp" as fraulein. (TV: The Daleks' Master Plan) It was also used as a title as in the case of Fraulein Dorothy Schmidt and Fraulein Bernice Summerfield. (PROSE: Timewyrm: Exodus, White Darkness)