When is a poem not a poem?

What makes a poem a poem? Poems by e. e. cummings and Stephen Crane e. e. cummings plato told him:he couldn’t believe it(jesus told him;he wouldn’t believe it)lao tsze certainly told him,and general (yes mam) sherman; and even (believe it or not)you told him:i told him;we told him (he didn’t believe it,no sir)it took a nipponized bit of the old sixth avenue el;in the top of his head:to tell him…