The 14-line verse form common in English poetry and used in Shakespeare’s sequence is the sonnet.
A sonnet traditionally contains fourteen lines, though its rhyme scheme and structure vary by tradition. The Italian, or Petrarchan, sonnet usually divides into an eight-line octave and a six-line sestet. The English sonnet developed a different pattern: three quatrains followed by a concluding couplet.
Shakespeare’s 154 sonnets generally use iambic pentameter and the English rhyme scheme ABAB CDCD EFEF GG. The quatrains often develop an argument, image, or emotional complication, while the final couplet frequently offers a turn, summary, or twist. This structure is why “Shakespearean sonnet” and “English sonnet” are often used interchangeably.
A common mix-up is confusing a sonnet with a villanelle. A villanelle has nineteen lines and repeated refrains, while a limerick normally has five lines. Shakespeare’s sonnets were published together in 1609, although individual poems may have been written earlier and their exact sequence of composition remains uncertain.