There are two types of sonnets: the Italian or Petrarchan, and the English or Shakespearean. The Italian sonnet consists of an octave, eight lines with the rhyme scheme "abbaabba," and a sestet, six lines with the rhyme scheme "cdcdcd." This means that the words at the end of the first line (a) and the fourth line rhyme, the words at the end of the second and third lines rhyme with each other but not with the first and fourth, and so forth. The English or Shakespearan sonnet consists of three quatrains, or 4-line stanzas, with the rhyme scheme "abab," and a couplet, which is simply two lines that end in rhyming words. Shakespeare's Sonnet XVIII, which begins, "Shall I compare thee to a summer's day?" is among the best known examples of the English or Shakespearan sonnet. Edna St. Vincent Millay's Sonnet XLIII, which begins, "What lips my lips have kissed, and where, and why," is a well-known example of the Italian or Petrarchan sonnet.
Ballads are narrative poems, or poems that tell stories. The rhyme scheme is typically four lines with the pattern "abab" or "abcb." There are four accented syllables in the first and third lines and three in the second and fourth lines. Sometimes they also include a refrain, like the chorus in a song. They are often anonymous and are handed down orally. In times past, when books were uncommon and even nonexistent, stories were sometimes preserved and handed down in the form of ballads. The form is still occasionally used creatively and attributed to authors today.
A villanelle is a poem with six stanzas, or verses. These are in the form of of five tercets, or 3-line verses and a quatrain. The rhyme scheme is "aba aba aba aba abaa." Each line has five stresses. The meter tends to be iambic, meaning that it is divided into 2-syllable units, or feet, with the stress on the second syllable. "Do Not Go Gentle Into that Good Night" by Dylan Thomas is a villanelle. An example of iambic meter is the first line: "Do not go gentle into that good night..."
Free verse poetry is poetry without rhyme or traditional structure. Each line does not have the same number of syllables, as in sonnet forms. Each line or every other line does not end with rhyming words. This less restrictive form relies more on literary devices such as imagery and metaphor, likening one thing to another, for its effect. These devices are used in more formal forms as well, but are useful to anchor a free verse poem that doesn't have the helpful constraints of formal verse. Free verse is also called "free form" or "open form." It is not the same as "blank verse," which, according to "The College Handbook of Creative Writing," is composed in iambic pentameter though the lines are not rhymed.