Poetic form, also known as "English sonnet", consisting of fourteen lines in iambic pentameter rhyming abab cdcd efef gg. Typically, a poet will introduce some subject in the first quatrain, develop it in the second and third, then reply to it in the final couplet.
For example:
Sonnet CXXXVIII
This is somewhat similar to the Japanese RenGa form, where a series of poems are linked together, starting with a 5/7/5 syllable poem, followed by a 7/7 syllable poem, replied to by a 5/7/5 poem. This last is the origin of the HaiKu form.
Compare to PetrarchanSonnet.
The term sonnet came into English via Italian from the Provençal sonet, a little poem, from son song, from Latin sonus a sound.