Fixed formats demand the poet abide by strict rules. For example, a sonnet must be 14 lines long. In a Petrarchian sonnet, the 14 lines are divided into two sections, and the last six lines have a required rhyming pattern. By contrast, a sestina must have six stanzas made up of six lines each. A villanelle begins with five three-line stanzas and ends with a quatrain, or four-line stanza.
Long formats include epic poems and ballads. An epic is generally an account of the epic battles of a heroic protagonist. Such poems can go on for a very great length. "Beowulf" is 3,183 lines (top 10 epics) and "The Aeneid" is 12 books long. Ballads are poems that started off as songs, such as "Barbara Allen." In long poem formats, the story plays an important role.
An ode is a form of poem that contemplates, and generally celebrates, a particular person or thing. Odes may vary in meter or rhyme scheme, but most are short and focused. Examples include John Keats' "Ode to a Nightingale" and Samuel Taylor Coleridge’s “Dejection: An Ode."
Some poetry formats are intentionally very short. The Japanese form of poetry known as haiku contains only three lines, none of them rhyming. A limerick, which is a generally humorous short poem, has five lines, usually with an AABBA rhyming pattern. One of the shortest formats is the epigram, which is a witty, brief poem that may only have two lines.
Free verse is an unstructured type of poem. T.S. Eliot, Ezra Pound, William Carlos Williams and many contemporary poets use free verse. In this format, the lines are non-metrical and nonrhyming, yet often free verse has a distinctive sound to it that separates it from normal spoken words. With free verse, the poem's title is important in conveying nuance.