What is Poetry?

Borrowed from Wikipedia
Poetry
is a form of literature that uses aesthetic and rhythmic qualities of language—to evoke meanings in addition to, or in place of, the prosaic ostensible meaning.
Poetry uses forms and conventions to suggest differential interpretation to words, or to evoke emotive responses. Devices such as assonance, alliteration, onomatopoeia and rhythm are sometimes used to achieve musical or incantatory effects. The use of ambiguity, symbolism, irony and other stylistic elements of poetic diction often leaves a poem open to multiple interpretations. Similarly figures of speech such as metaphor, simile and metonymy create a resonance between otherwise disparate images—a layering of meanings, forming connections previously not perceived. Kindred forms of resonance may exist, between individual verses, in their patterns of rhyme or rhythm.
Some poetry types are specific to particular cultures and genres and respond to characteristics of the language in which the poet writes. Readers accustomed to identifying poetry with Dante, linewGoethe, Mickiewicz, and Rumi may think of it as written in lines based on rhyme and regular meter; there are, however, traditions, such as Biblical poetry, that use other means to create rhythm and euphony. Much modern poetry reflects a critique of poetic tradition, playing with and testing, among other things, the principle of euphony itself, sometimes altogether forgoing rhyme or set rhythm.
In today's increasingly globalized world, poets often adapt forms, styles and techniques from diverse cultures and languages.
Meter
In the Western poetic tradition, meters are customarily grouped according to a characteristic metrical foot and the number of feet per line.
There is debate over how useful a multiplicity of different "feet" is in describing meter. Actual rhythm is significantly more complex than the basic scanned meter described above, and many scholars have sought to develop systems that would scan such complexity. Vladimir Nabokov noted that overlaid on top of the regular pattern of stressed and unstressed syllables in a line of verse was a separate pattern of accents resulting from the natural pitch of the spoken words, and suggested that the term "scud" be used to distinguish an unaccented stress from an accented stress.
Metrical patterns
Different traditions and genres of poetry tend to use different meters, ranging from the Shakespearean iambic pentameter and the Homeric dactylic hexameter to the anapestic tetrameter used in many nursery rhymes.
Rhyme, alliteration, assonance
Rhyme, alliteration, assonance and consonance are ways of creating repetitive patterns of sound. They may be used as an independent structural element in a poem, to reinforce rhythmic patterns, or as an ornamental element.
Rhyme consists of identical ("hard-rhyme") or similar ("soft-rhyme") sounds placed at the ends of lines or at predictable locations within lines. Languages vary in the richness of their rhyming structures; Italian, for example, has a rich rhyming structure permitting maintenance of a limited set of rhymes throughout a lengthy poem. The richness results from word endings that follow regular forms. English, with its irregular word endings adopted from other languages, is less rich in rhyme
Alliteration is the repetition of letters or letter-sounds at the beginning of two or more words immediately succeeding each other, or at short intervals; or the recurrence of the same letter in accented parts of words. Alliteration and assonance played a key role in structuring early Germanic, Norse and Old English forms of poetry. The alliterative patterns of early Germanic poetry interweave meter and alliteration as a key part of their structure, so that the metrical pattern determines when the listener expects instances of alliteration to occur. This can be compared to an ornamental use of alliteration in most Modern European poetry, where alliterative patterns are not formal or carried through full stanzas. Alliteration is particularly useful in languages with less rich rhyming structures.
Assonance, where the use of similar vowel sounds within a word rather than similar sounds at the beginning or end of a word, was widely used in skaldic poetry.
Rhyming schemes
Most rhyme schemes are described using letters that correspond to sets of rhymes, so if the first, second and fourth lines of a quatrain rhyme with each other and the third line does not rhyme, the quatrain is said to have an "a-a-b-a" rhyme scheme. Similarly, an "a-b-b-a" quatrain (what is known as "enclosed rhyme”) is used in such forms as the Petrarchan sonnet. Some types of more complicated rhyming schemes have developed names of their own, separate from the "a-b-c" convention.
Form
Poetic form is more flexible in modernist and post-modernist poetry, and continues to be less structured than in previous literary eras. Poetry remains distinguished from prose by its form; some regard for basic formal structures of poetry will be found in even the best free verse, however much such structures may appear to have been ignored.
Among major structural elements used in poetry are the line, the stanza or verse paragraph, and larger combinations of stanzas or lines such as cantos. These basic units of poetic form are often combined into larger structures, called poetic forms or poetic modes (see following section), as in the sonnet or haiku.
Lines and stanzas
Poetry is often separated into lines on a page. These lines may be based on the number of metrical feet, or may emphasize a rhyming pattern at the ends of lines. Lines may serve other functions, particularly where the poem is not written in a formal metrical pattern. Lines can separate, compare or contrast thoughts expressed in different units, or can highlight a change in tone.
Lines of poems are often organized into stanzas, which are denominated by the number of lines included. Thus a collection of two lines is a couplet(or distich), three lines a triplet (or tercet), four lines a quatrain, and so on.
In many forms of poetry, stanzas are interlocking, so that the rhyming scheme or other structural elements of one stanza determine those of succeeding stanzas.