Japanese oak vs oak

Japanese oak and oak both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese oak	Yes	No	No	No
oak	Yes	No	No	No

As nouns, oak is a hypernym of Japanese oak; that is, oak is a word with a broader meaning than Japanese oak:

Other hypernyms of Japanese oak include oak tree.

Japanese oak (noun)	oak (noun)
small evergreen tree of China and Japan	a deciduous tree of the genus Quercus; has acorns and lobed leaves
oak with moderately light fine-grained wood; Japan	the hard durable wood of any oak; used especially for furniture and flooring