(With thank yous to Tony Brown for passing this along.)
Clicky on the ‘toon to go see it (bigger, more legible) on qwantz.com.
The Sonnet, according to Wikipedia:
A sonnet is one of several forms of poetry that originate in Europe, mainly Provence and Italy. They commonly contain 14 lines. The term “sonnet” derives from the Occitan word sonet and the Italian word sonetto, both meaning “little song” or “little sound”. By the thirteenth century, it signified a poem of fourteen lines that follows a strict rhyme scheme and specific structure. Conventions associated with the sonnet have evolved over its history. Writers of sonnets are sometimes called “sonneteers,” although the term can be used derisively. One of the best-known sonnet writers is William Shakespeare, who wrote 154 of them (not including those that appear in his plays). A Shakespearean, or English, sonnet consists of 14 lines, each line containing ten syllables and written in iambic pentameter, in which a pattern of an unstressed syllable followed by a stressed syllable is repeated five times. The rhyme scheme in a Shakespearean sonnet is a-b-a-b, c-d-c-d, e-f-e-f, g-g; the last two lines are a rhyming couplet.
Traditionally, English poets employ iambic pentameter when writing sonnets, but not all English sonnets have the same metrical structure: the first sonnet in Sir Philip Sidney‘s sequence Astrophel and Stella, for example, has 12 syllables: it is iambic hexameters, albeit with a turned first foot in several lines. In the Romance languages, the hendecasyllable and Alexandrine are the most widely used metres.
The Iamb, also according to Wikipedia:
An iamb (/ˈaɪæm/ or iambus) is a metrical foot used in various types of poetry. Originally the term referred to one of the feet of the quantitative meter of classical Greek prosody: a short syllable followed by a long syllable (as in delay). This terminology was adopted in the description of accentual-syllabic verse in English, where it refers to a foot comprising an unstressed syllable followed by a stressed syllable (as in a-bove).