In terms of meaning, I will classify poems into 4 categories:
Category I: This is the poem that consists of just pretty words with no underlying deeper meaning; it is intended to convey an aesthetic impression and nothing more.
Catergory II: This is the poem which has a determinable meaning, either on plain reading or on analysis, but determinable without recourse to the poet's life.
Category III: This is the poem that has multiple meanings, none of which is 'objectively' true, such that the reader can ascribe any meaning to it of his own fancy.
Category IV: This is the poem that is intended by the poet to be a metaphorical expression of a particular feeling, experience or life-event. I would call it the 'objective meaning' of the poem.
Whenever I read a poem, my first question is: Which category does this poem belong to? How do we even decide which poem belongs to which category?
Category II has the determinable meaning, so that is easiest to identify (though it too can cause confusion if it is too obscure), so the actual problem is with other categories, and they are what I'll discuss from this point onwards. Category IV would be easy to identify if the poet reveals that the poem is about this or that experience, but if the poet publishes the poem in isolation without revealing the underlying experience, then the reader is left lost, the poem becomes any of the category I or III for the reader. It can even be the other way round. If, for example, I write a poem of Category I while I am going through a break-up, a friend of mine may mistakenly believe that the poem belongs to Category IV and is an expression of my feelings of break-up, while that is not actually so.
The point is, unless the poet himself reveals what the poem is about, the reader is free to judge the poem as belonging to any category he thinks appropriate. When a poem is published in isolation, the objective meaning of the poem is lost, and the poem becomes a matter of complete subjective interpretation, capable of being fit in any category the reader believes it to belong to. The poet abandons a poem to subjectivity by withholding the objective meaning. Of course, people can and do argue that this very subjectivity is what makes poetry what it is. If that is so, well, then that is so. The question of "What does it mean?" becomes irrelevant, because the answer to that is "It means whatever you want it to mean."