salvia vs herb

salvia and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
salvia	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of salvia; that is, herb is a word with a broader meaning than salvia:

salvia: any of various plants of the genus Salvia; a cosmopolitan herb
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of salvia include herbaceous plant.

salvia (noun)	herb (noun)
any of various plants of the genus Salvia; a cosmopolitan herb	aromatic potherb used in cookery for its savory qualities
	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests