The volta, which literally translated from Italian means "turn," is a device used to change the tone or thought in a sonnet, and it is used differently depending on whether the sonnet is Italian, where the volta will be after the first octave, or Shakespearean, where it used before the final couplet, in style. Almost all traditional sonnets, especially more classical poems, will feature a volta.
There are a number of subtle differences between the Shakespearean sonnet and the Italian, or pertrarchal, sonnet in addition to where the volta will appear.
A Shakespearean sonnet is traditionally composed of three quatrains with a rhyming scheme of abab, cdcd, efef, gg. The volta is located before the final couplet, where the argument or thought is summed up by the poet with the final lines.
Italian sonnets are broken down into two sections, the octave (the first eight lines), followed by a sestet (the final six-line section). Octaves usually use the rhyming scheme of abbaabba, followed by the volta. In Italian sonnets, the volta also signals a quantifiable change in rhyming scheme, and it is arguably more pronounced than in a Shakespearean sonnet as a result. The final sestet scheme can vary, and schemes may include cdcede, cdedce, or cdcdcd.