An Italian sonnet is a type of poem that has two sections. It is a rhymed sequence that follows the pattern of a b b a a b b a. Clearly, the second section of the poem begins with the third 'a'. The change in section of the poem reflects a change in the subject matter. Usually, this means a shift in the tone of the poem as well.
The Italian sonnet is around 14 lines on average; 7 lines in the first section and 7 in the second. Many times the end of the Italian sonnet is a broken sentence or one that includes an en dash (--). Sometimes the rhyming pattern could be changed to a b b a a c c a, which removes the need for two sections of the poem. Either way works, though most people prefer the a b b a a b b a style to the a b b a a c c a style because the latter is classic and more well-known.
A sonnet consisting of an octave with the rhyme pattern abbaabba followed by six lines with a rhyme pattern of cdecde or cdcdcd.