A sonnet is a short lyric poem of fourteen iambic pentameter lines linked by an intricate rhyme scheme. It is a lyric because it can be tuned to a lyre, a musical instrument. Each of its fourteen lines consists of five feet (also known as meters) for which it is called pentameter.
Again, each of the feet consists of an unaccented syllable and an accented syllable (of sound unit) for which it is called iambic. It is of three types: Petrarchan or Italian, Spenserian, and Shakespearean. The first eight lines of a Petrarchan sonnet are called octave and the last six lines are called sestet.
A Petrarchan sonnet rhymes as abababab cdcdcd or abababab cdecde. Wordsworth’s “The World is too Much with Us” is an example of Petrarchan sonnet.
A Spenserian sonnet rhymes as abab bcbc cdcd ee. A Shakespearean sonnet rhymes as abab cdcd efef gg. Shakespeare’s “Sonnet- 18” is an example of a Shakespearean sonnet.