Which basic prosodic units make up a poem’s metrical structure?

In the study of prosody, a poem’s metrical structure is built upon three fundamental units: the foot, the line, and the stanza.1

• Foot: The smallest metrical unit, a foot consists of a specific combination of stressed and unstressed syllables. In English verse, the prevailing type of foot—such as the iamb, trochee, anapest, or dactyl—is determined through scansion.213
• Line: The metre of a poem is defined by the kind and number of feet contained within each line (e.g., iambic pentameter, which features five iambic feet).21
• Stanza: This unit represents a recurring set of lines, often organized by a specific rhyme scheme and metrical pattern, which helps structure the poem as a whole.1

While these units provide the framework for regular metre, poets may also employ substitutions—replacing one type of foot with another—to create tension or variety within the established rhythm.1