A sonnet is a type of poem that has its origins in Italy during the 13th century. It was made popular by the Italian poet Petrarch, whose sonnets were later translated and imitated by English poets like Thomas Wyatt and Henry Howard, Earl of Surrey. The most famous sonneteer in English literature is William Shakespeare, who wrote 154 sonnets in the early 17th century.

The sonnet is a 14-line poem, usually written in iambic pentameter, with a specific rhyme scheme. There are two main types of sonnets: the Italian or Petrarchan sonnet, which is divided into an octave (eight lines) and a sestet (six lines), with a rhyme scheme of abbaabba for the octave and cdecde or cdcdcd for the sestet; and the English or Shakespearean sonnet, which is divided into three quatrains (four-line stanzas) and a final couplet (two lines), with a rhyme scheme of abab cdcd efef gg.

Sonnets are often used to explore themes of love, beauty, and the passage of time. They are also used to express personal thoughts and emotions, as well as to reflect on political and social issues. The sonnet's strict structure makes it a challenging form for poets, but also allows for creative expression within its constraints.

Sub-categories of sonnets include the Spenserian sonnet, which has a different rhyme scheme and interlocking quatrains, and the Miltonic sonnet, which is similar to the Petrarchan sonnet but with a more flexible rhyme scheme. Sonnets continue to be a popular form of poetry today, with modern poets experimenting with the form and using it to address contemporary issues.