What is poetry?
There's more to consider about poetry than just its definition. When we want to write down our thoughts, there are essentially three choices: list, prose, or poetry. A list is just that--a series of words which have a fairly loose connection and there is no real attempt to communicate anything with them beyond the obvious. Prose is anything written in sentence form, ranging from a paragraph to a novel. In prose, writers can utilize images as well as words to create meaning. The structure of prose is such that there are rules and conventions to which writers must generally conform.
Poetry, though, is another form of expression entirely. It uses words and phrases, senses, and imagery--generally in their most condensed, compressed, or compact forms--to create meaning. All the extraneous elements are omitted, leaving those words and images to draw a picture for the reader. It may be more or less structured, but it's a condensation of longer and more wordy prose and the effect is generally much more powerful.
Poetry is figurative language in both rhymed and unrhymed forms. It is intended for an audience that enjoys the figurative form that comes from metaphors, similes, and other literary devices. It conveys emotion at all times, as it does not describe factually but, once again, figuratively.
Poetry can come in a diversity of meters and styles, one famous one being a "ballad," which resembles in rhythm the closest thing to a song. The most important thing about poetry is its rich use of metaphors, the appeal to the most nostalgic and sentimental of our senses, and the fact that it has inspired millions since the beginnings of history as a way to express what is real and what is not.