Poa nemoralis vs meadow grass

Poa nemoralis and meadow grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Poa nemoralis	Yes	No	No	No
meadow grass	Yes	No	No	No

As nouns, meadow grass is a hypernym of Poa nemoralis; that is, meadow grass is a word with a broader meaning than Poa nemoralis:

Poa nemoralis: slender European grass of shady places; grown also in northeastern America and temperate Asia
meadow grass: any of various grasses that thrive in the presence of abundant moisture

Other hypernyms of Poa nemoralis include meadowgrass.

Poa nemoralis (noun)	meadow grass (noun)
slender European grass of shady places; grown also in northeastern America and temperate Asia	any of various grasses that thrive in the presence of abundant moisture