Poetry - my thoughts;
Poetry is like art and music. It may make you feel. It may invoke beautiful images. It may make you see something in a new way. It may reflect your life and experiences so you relate to the poem and it becomes personal. Good poetry can do this without you totally understanding it. As with music, which can make you feel even if you do not know the notes and expressions of the music, you need not understand every device, image or implication used by the poet to receive the effect of the poem. Of course understanding them will add to your appreciation.
I used the quotes because they say things that I agree with about poetry.(a lot of these apply to quotations as well)
Putting my interpretation of these quotes into my own “plain English” words (as in the order above);
Poetry is joy, pain and wonder in words.
Poetry is ideas and emotions held together by words.
Poetry is thoughts and words that come alive and affect you.
Poetry is using meaning, rhythm, meter and other poetical devices to make images and feelings of beauty.
Poetry is more than the sum of its parts. You cannot define what it is that makes it work. The best poetry leaves enough room for the reader to flavour it with their own experiences and perceptions and make it personal.
Poetry is a way of trying to understand and deal with life.
I probably should leave it to Phaedrus to comment on his quotes (if he wishes) but I enjoyed all the quotes and will comment on these two;
Poetry is that stuff in books which doesn't quite reach to the margin
~Schoolchild
Sometimes that is the only way to tell that it is poetry!

Poetry is a raid on the inarticulate
~T.S. Eliot
I think that this one sums it up best of all. Poetry is trying to express all those things that we cannot articulate – beauty, pain, emotion, life and its meaning. Everything.