A poem is whatever you, as a writer, persuade a particular reader to experience as a poem.
Some readers are convinced all of the time: they will gush equally over Jack Kerouac and every imitator at the neighborhood open mic, as wel las Rod McKuen, Hallmark cards, and at least some advertising copy.
Some poetry convinces almost everybody: The Twenty-Third Psalm ;Dylan Thomas's "Do Not Go Gentle Into That Good Night"; Eugene Field's "The Duel"; some of the classic haiku, don't yell at me if I forgot yourfavorite just plug it in here yourself.
Some people will never be convinced by any work unless it is iambic pentameter and rhymes; or it contains a seasonal word; or it refers only to emotion and subjective experience; or it refers only to external, objective experience; or an infinite range of other specific criteria.
There is more than one kind of poet in the world because there is more than one kind of reader in the world.
Myself, I am in favor of craftsmanship and working on a poem -- not just spilling my guts on a page and calling it good.
But I don't think any of the technical criteria in the world will save you if you haven't got any guts in there to begin with. There has to be some heart, soul, insight, or feeling to spark a poem, to make it worth writing and worth reading -- and that is the essence of what reaches up and grabs a reader, what makes someone say, "That's a poem."
And be content if at least some of the readers in the world respond to you. If twenty people tell you "I can't make head or tails of this", please consider re-write. If ten people cry because they did understand you, and ten others are still scratching their heads -- be content with the audience that you speak to. If you don't bother trying to please or communicate with anyone, you are not a poet; you are masturbating with a pencil. But if you try to please everyone, you'll end up pleasing none.
"And remember, my child: if you are afraid to write a bad poem,
you will never write a good one."