caviar vs beluga caviar

caviar and beluga caviar both are nouns.

Word	Noun	Adjective	Verb	Adverb
caviar	Yes	No	No	No
beluga caviar	Yes	No	No	No

As nouns, beluga caviar is a hyponym of caviar; that is, beluga caviar is a word with a more specific, narrower meaning than caviar:

caviar: salted roe of sturgeon or other large fish; usually served as an hors d'oeuvre
beluga caviar: roe of beluga sturgeon usually from Russia; highly valued

caviar (noun)	beluga caviar (noun)
salted roe of sturgeon or other large fish; usually served as an hors d'oeuvre	roe of beluga sturgeon usually from Russia; highly valued