German shepherd vs sheep dog

German shepherd and sheep dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
German shepherd	Yes	No	No	No
sheep dog	Yes	No	No	No

As nouns, sheep dog is a hypernym of German shepherd; that is, sheep dog is a word with a broader meaning than German shepherd:

German shepherd: breed of large shepherd dogs used in police work and as a guide for the blind
sheep dog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of German shepherd include sheepdog, shepherd dog.

German shepherd (noun)	sheep dog (noun)
breed of large shepherd dogs used in police work and as a guide for the blind	any of various usually long-haired breeds of dog reared to herd and guard sheep