And the answer: sonnet.
Sonnets are named from the Italian "sonetto," which means "a little sound or song." There are many different types of sonnets, but all of them have fourteen lines and follow iambic pentameter. Italian, or Petrarchan sonnets consist of an octave followed by a sestet: eight lines followed by six lines. English, or Shakespearean sonnets consist of three quatrains and a couplet.
The history of sonnets dates back to 13th century Italy, to a man named Giacomo da Lentini. The style spread quickly throughout Europe after its inception, and eventually Lentini’s fame was eclipsed by another up-and-coming Italian poet: Petrarch. Petrarch’s famous collection, Il Canzoniere, features 317 sonnets written in adoration of a woman named Laura. This romantic, unrequited love informed Petrarch’s style so much so that it earned itself a distinct categorization: Petrarchism. This style of poetry features an intense yet unattainable love and is often riddled with similes, metaphors, and vivid descriptions. Later, the Petrarchan sonnet came to be synonymous with the Italian sonnet.
Regardless of their place of origin, all sonnet styles are written in iambic pentameter. This is a poetic style which seeks to imitate natural speech patterns. An “iamb” refers to words which have two syllables and emphasize the second syllable. Examples of iambs include words such as “prepare,” “secure,” or “insist.” Meanwhile, “pentameter” counts the number of iambs in a line, which is—you guessed it—five per line. When put all together, iambic pentameter should replicate the rhythm of a human heartbeat (think: ba dum, ba dum, ba dum).
Another key element of the sonnet is the volta, or turn. The turn is a thematic convention, rather than the structural requirement of iambic pentameter. Broadly speaking, sonnets tend to present one topic, theme, or argument, before then turning to consider another perspective, counter-argument, or idea that undermines that topic completely. In many Italian sonnets, this turn can be found at the beginning of the sestet and is often marked by words such as “but” or “yet.” Meanwhile, in many English sonnets, the turn can be found in the final couplet.
Learn more about sonnets throughout history here.