poem vs concrete poem

poem and concrete poem both are nouns.

Word	Noun	Adjective	Verb	Adverb
poem	Yes	No	No	No
concrete poem	Yes	No	No	No

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

poem: a composition written in metrical feet forming rhythmical lines
concrete poem: a poem whose meaning is conveyed through its graphic shape or pattern on the printed page.

poem (noun)	concrete poem (noun)
a composition written in metrical feet forming rhythmical lines	a poem whose meaning is conveyed through its graphic shape or pattern on the printed page.