Definition of Octave
Octave has been derived from the Latin word octāva, which means “eighth element.” It is a verse form that includes eight traces, which commonly appear in an iambic pentameter. In simple words, it can be any stanza in a poem that has eight traces and follows a rhymed or unrhymed meter.

Types of Octave
Each stanza of this verse shape follows rhyme scheme of a, b, a, b, c, d, c, D. Or a, b, a, b, c, b, c, B. The last line might also repeat any meter.
It seems in quatrains with uneven couplets and ends with a declamatory rhyming couplet. It follows alternating iambic pentameter and iambic dimeter strains. The rhyme scheme is: xaxa xbxb xcxc, where x is unrhymed.
Ottava Rima
This shape of octave contains eight lines, which normally seem in iambic pentameter sample. Each stanza contains three trade rhyming lines with one double rhyme. It follows rhyme scheme of a-b-a-b-a-b-c-c.
Sicilian Octave
This verse form contains eight lines with eleven syllables, known as hendecasyllable in Italian. It follows the rhyme scheme of a-b-a-b-a-b-a-b.
Italian or Petrarchan Octave
Initially, it did no longer follow any set rhyming patter; however, later on it followed iambic pentameter with rhyme scheme of a-b-b-a-a-b-b-a.
Hymnal and Common Octave
It follows rhyming pattern a-b-c-b-a-b-c-b. The first one uses iambic tetrameter and the second one one uses iambic trimeter.
Sometimes it's miles in the form of loose or blank verse or unusual pattern. However, the most common rhyming pattern for this verse form is a-b-b-a-a-b-b-a.
Huitain includes 8 or 10 syllables with each line having rhyming pattern of a-b-a-b-b-c-b-c or a-b-a-b-a-c-a-c
Sicilian Octave
It does not have a set form, but normally follows rhyming pattern of a-b-a-b-a-b-a-b.
Strambotto Tuscano
It follows rhyme scheme of a-b-a-b-a-b-c-c. Each line contains eleven syllables.
Strambotto Siciliano
It makes use of a rhyming sample a-b-a-b-a-b-a-b. There are eleven syllables in each line.
Strambotto Romagnuolo
It uses rhyme scheme of a-b-a-b-c-c-d-d with eleven syllables in every line.
Unwreathed Octave
It also makes use of double rhymes with outside rhyme as b-a-b-d-c-d-c and Internal rhyme a-b-a-c-d-c-x. There is not any set meter.
Wreathed Octave
It also has double rhymes with outside rhyme as a-b-a-b-c-d-c-d and inner rhyme follows the sample of x-a-b-a-d-c-d-c.
Examples of Octave in Literature
Example #1: The New Colossus (By Emma Lazarus)
‘Not just like the brazen massive of Greek fame,
With conquering limbs astride from land to land;
Here at our sea-washed, sundown gates shall stand
A mighty lady with a torch, whose flame…
The air-bridged harbor that twin towns frame.

This is an instance of Petrarchan Octave, which follows the rhyme scheme of a-b-b-a-a-b-b-a. It is the first a part of Petrarchan or Italian sonnet.

Example #2: Of the Gentle Heart (via Guido Guinicelli)
Within the gentle coronary heart Love shelters him
As birds inside the green shade of the grove.
Before the gentle coronary heart, in nature’s scheme,
Love was now not, nor the mild heart ere Love…
And Love has his impact in gentleness.

This stanza affords an instance of Canzonetta, a verse shape that uses rhyming pattern of a, b, a, b, c, d, c, D.

Example #3: Filiocola (by means of Giovanni Boccaccio)
Qui, d’Atropos il colpo ricevuto,
giace di Roma Giulia Topazia,
dell’alto sangue di Cesare arguto
discesa, bella e piena d’ogni grazia…
Dio biasimar che fè sí gran fallazia.

Boccaccio has used this eight-line verse Sicilian Octave in his earlier poem Filiocola. This form follows rhyme scheme of a-b-a-b-a-b-a-b.

Example #4: Sonnet 16 (by means of John Milton)
When I bear in mind how my mild is spent
Ere half my days in this dark global and wide,
Lodg’d with me useless, even though my soul greater bent…
“Doth God exact day-labour, mild denied?”
I fondly ask. But Patience, to prevent…

This is an example of octave, that is the first part of Italian sonnet that ends with a contrasting sestet. It generally uses a metrical sample of iambic pentameter, five iambs in each line, that's proven as underlined inside the second closing line.

Function of Octave
An octave serves as a musical interval or performs the position of a brief distance between musical notes. In fact, it's far a distance between two notes with comparable letter names. In poetry, it represents eight strains of a poem, often the first a part of a sonnet, wherein it poses questions, whilst the second component, sestet, solutions them. To placed it in easy words, an octave provides a quandary or a hassle within the first component, which, sestet, as the second one part resolves.
Novella Ode