Final answer:
The last six lines of a Petrarchan sonnet are called a sestet, which follows the initial eight-line octave and features various rhyme schemes.
Step-by-step explanation:
The last six lines of a Petrarchan sonnet are called a sestet. In a Petrarchan or Italian sonnet, the poem is divided into two parts: the first is an octave, consisting of eight lines with a rhyme scheme of abbaabba.
The second part is the sestet, with various rhyme schemes such as cdcdcd or cdecde. The volta, or turn in thought, conventionally appears after the octave.
The sestet serves as a resolution or counterpoint to the issue or question presented in the octave, and it is where the poet typically delivers the thematic conclusion or emotional resolution to the poem.