Stanzas are categorized by their line count, and each count has its own name. Two lines form a couplet, three lines create a tercet, and four lines make a quatrain — the most common stanza type in English poetry. Five lines are called a cinquain, six lines make a sestet, seven lines create a septet, and eight lines form an octave. For stanzas longer than eight lines, they’re typically named by their line count (like nine-line or ten-line) or by the specific poetic form they belong to, such as the Spenserian stanza.
Stanzas can be either fixed or free. A fixed stanza maintains the same line count, rhyme scheme, and often the same meter throughout the poem — classic examples include the ballad quatrain and the Spenserian stanza. In contrast, a free stanza varies in length from one section to another, guided by the poet's intuition about where one thought ends and another begins.
The term itself comes from the Italian word for "room," which is an apt metaphor. Each stanza serves as a room in the poem's structure: it has walls (the blank lines), a specific purpose, and a connection to the stanzas adjacent to it. This tradition stretches from ancient Greek odes to medieval ballads, through Shakespeare's sonnets, and into the works of Keats and Dickinson, among others. Stanzas endure because they provide readers a place to pause and allow poets a structured unit to work with.