Belgian shepherd vs sheep dog

Belgian shepherd and sheep dog both are nouns.

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

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

Belgian shepherd: hardy working dog developed in Belgium for herding sheep
sheep dog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of Belgian shepherd include sheepdog, shepherd dog.

Belgian shepherd (noun)	sheep dog (noun)
hardy working dog developed in Belgium for herding sheep	any of various usually long-haired breeds of dog reared to herd and guard sheep