See Also: A Brief Glossary of Meter
The term stanza means “stopping place” in Italian. A stanza is a set of lines in a poem, set apart from other sets of lines by space. Each stanza comprises its own unit. The break/space between stanzas generally indicates a pause between thoughts, concepts or actions. In standard practice, most poems end a sentence at the end of stanza. It is important to remember, however, that there is no definitive rule that says this must happen. Of all writing forms, poetry is the most experimental. Rules of form get broken all the time.
Many poems are written without stanza breaks. These poems simply continue for however many lines the poem lasts. It is possible to call these poems single-stanza poems, but in practice few people worry about any rules or guidelines for stanzas in these cases.
Most poetry forms have rules regarding the length of stanzas. For example, a sestina has seven stanzas. The first six are six lines long and the last is three lines long. A sestina has many other rules involving repetition and order of words, but stanzas are the primary concern here.
Stanzas provide structure and format within a poem. In many ways they are the equivalent of a paragraph in a prose work. The use of stanzas can make a poem more visually appealing, and give the poem a means of division. Even poems without rhyme or meter will gain structure from the use of stanzas.
Stanzas can take many forms, most of which are unnamed. A few standard stanzas have stood the test of time. A couplet is a two-line stanza; if the two lines rhyme it is called a rhyming couplet. A tercet or triplet is a three-line stanza. A quatrain is a four-line stanza. Sometimes a stanza is called a verse or a stroph. The meaning is essentially the same, but stanza is the far more popular term.
The important thing to remember is that, except when you are using a set form, you have a great deal of leeway in how you use stanzas. You can set stanzas to break at the end of every sentence, every action, or every independent thought, for example. Unless a particular form demands it, you should simply divide your poems up in ways that make sense to you. A stanza can vary in number of lines and in line length or meter. Using multiple stanzas is simply a way to bring structure to your poem.