Au contraire!! I'm going to have to comment again!

Of course a definition is unique - it has to be 'by definition'. If a definition is not unique then all language becomes useless because every word can have a meaning given it by the person who uses it. We'd lose the ability to communicate altogether!

Hence why there must be a definition of poetry that enables it to be differentiated from normal prose.

I'd agree with you with the preference for straightforward poetry though. I quite like the poems with clever hidden meanings which are open to interpretation (that you mentioned earlier) but what I like about them is the one definite thing that I see in them!