Final answer:
The transition between the two sections of a Petrarchan sonnet is known as the volta, marking a shift in the poem's argument or focus.
Step-by-step explanation:
The switch between the two parts of a Petrarchan sonnet is called the volta, which is Italian for 'turn.' The Petrarchan sonnet consists of an octave, with a rhyme scheme of ABBAABBA, and a sestet, which may have varying rhyme schemes. The volta occurs between the octave and the sestet, marking a shift in thought or argument within the poem. This turn is a critical feature of the sonnet, as it conventionally moves from presenting a problem, question, or situation in the octave to a resolution or contemplation in the sestet.