A short paragraph could answer the question, but let me fertilize the ground of the subject, carefully water the sonnet bush that we may enjoy the fragrance of its newest blossom.
The sonnet form in poetry was developed centuries ago in Italy, and Francesca Petrarca, Petrarch in English, gave it a great impetus with a series of poems. Started when he was 22 years of age, they are about a "Laura." By the time he was in his 50's he finished preparing the poems for publication as a 2 part series: "Rime in Vita de Laura," and "Rime in Morte de Laura." (Laura in Life, and Laura in Death) Most of the poems are sonnets; 14 lines of iambic pentameter beginning with an octave with only two rhymes carried through the 8 lines: abba,abba. The rhyme pattern of the sestet varied in 2 or 3 rhymes such as cd,cd,cd, cde,cde, or cdc,ede.
Various people have attempted translations of Petrarch's work. But remember that poetry is an art of language involving rhyme, meter, and many other elements of sound. Accurate translation of a poem is impossible.
The sonnet became popular in Italy and many wrote such poems. Even Michelangelo wrote sonnets, though we know him more as an artist and sculptor. During the Renaissance men of social status were expected to be skilled in every field from poetry to combat.
Two English noblemen who traveled in Italy, Sir Thomas Wyatt, and Henry Howard, Earl of Surrey, introduced the sonnet to England by translating Italian sonnets into English. Wyatt used the traditional Italian form. Howard created the English sonnet of 3 quatrains and a final couplet. This frees the poet from having to use four rhyming words as required by the Italian form. The English sonnet requires only two words for each rhyme since the pattern is abab,cdcd,efef,gg. This form is sometimes called a Shakespearean sonnet as well as English.
During the 1590's sonnet writing became popular among some of the English poets. A few translated sonnets from continental Europe, while others wrote original verse. Edmund Spenser set his sonnets apart with a unique form, the Spenserian sonnet, again requiring four rhyming words, but differing from the Italian form. The rhyme pattern is abab,bcbc,cdcd,ee.
My sonnet library includes translations of continental poets, complete works of the Elizabethans, selections of sonnets from different time periods, various commentaries about the sonnets, and even a sonnet concordance and Shakespeare glossary. Besides Shakespeare's sonnets, I've studied all the sonnets of Wyatt, Howard, Sidney, Spenser, Daniel, Drayton, Lodge, and Fletcher.
In my youth I tried my hand at writing sonnets just for fun. Like Spenser, I soon sought some new approach to set my poetry apart. After trying a few unusual rhyme patterns I settled for abac,bcbd,cdcb,db. This rhyme pattern is what I call the Ackerman sonnet (my name) or the American sonnet, assuming it might catch on with others. I've played with repeating lines, for example, repeating the second line as the last, trying to give it emphasis or a different meaning in the final line. Another possibility is to keep the last two lines of the octave and sestet the same, though reversed. Just as Shakespeare played with placing the traditional break in thought between the octave and sestet in different places, the American sonnet lends itself to different break locations. The rhyme allows a sestet – octave structure. I'm curious to see what others do with it.
Have fun with the American sonnet. Now you know why I go by "sonnetreader."