A heterometric poem or stanza is composed of lines of varying lengths and metrical structures. The opposite is an isometric stanza, which is a stanza composed of lines of equal length and metrical structure. In traditional poetry, there are a few types of heterometric stanzas, including the Sapphic and the Spenserian stanza. In poetry written since the early 20th century, heterometric stanzas are very common.
How it melts upon the ear,
How it nourishes the heart!
Cold, ah! cold must his appear,
Who hath never shared a part
Of woman’s love.
And this stanza from Hart Crane’s “Legend” (1924) is heterometric, composed of six lines of varying length and meter:
Twice and twice(Again the smoking souvenir,Bleeding eidolon!) and yet again.Until the bright logic is wonUnwhispering as a mirrorIs believed.