The Gale Student Resources in Context database defines poetry like this:
Poetry is a form of writing in which emotions and ideas are expressed through stylized, carefully crafted lines of text. Poetry is an art in which the author uses words as a medium. The author crafts the lines, words, and syllables to construct a specific format that evokes certain thoughts and emotions in the audience.
One way poetry differs from other forms of writing is that poems use words as sparingly as possible. Each word serves a specific purpose to crafting meaning in the poem. In fact, many poems' meanings could be altered by changing only a few words. The same is not generally true of prose or other types of writing.
The website poetry.org provides this definition:
Poetry (ancient Greek: ποιεω (poieo) = I create) is an art form in which human language is used for its aesthetic qualities in addition to, or instead of, its notional and semantic content. It consists largely of oral or literary works in which language is used in a manner that is felt by its user and audience to differ from ordinary prose.