A stanza is a recurring unit of a poem, consisting of a number of verses. The simplest form of stanza is the couplet; it is two lines rhyming together. A single couplet considered in isolation is sometimes called a distich; when it expresses a complete thougth, ending with a terminal mark of punctuation, it is called a closed couplet.
Another traditional and challenging form of couplet is the tetrameter, or four-beat couplet. Since a four-beat line is hard to divide by caesura without splitting it into two tick-tock dimeters, tetrameter couplets have posed a perpetual challenge to poets.
Terza rima (from Italian) consists of linked groups of three rhymes according to the following pattern: aba bcb cdc ded, etc.
Quatrains are stanzas of four lines; the lines usually rhyme alternately, abab, or in the second and fourth lines, abcb. When they alternate tetrameter and trimeter lines, they are called ballad stanza.
Rime royal is a severan-line iambic pentameter stanza consisting essentially of a quatrain dovetailed onto to couplets, according to the rhyme scheme ababbcc.
Closely akin to rime royal, but differentiated by an extra a-rhyme between the two b-rhymes, is ottava rima, that is, an eight-line stanza rhyming ababacc.
The Spenseriana stanza has nine lines rhyming ababbcbcc; the first eight lines are pentameter, the last line an Alexandrine. Slow-moving, intricate of pattern, and demanding in its rhyme scheme, the Spenseriana stanza has nontheless appealed widely to poets seeking a rich and complicated metrical from.
The sonnet, originally a stanza of Italian origin which has developed into an independent lyric form, is usually defined nowadays as fourteen lines of iambic pentameter.