upbeat: The unstressed syllable or syllables beginning a metrical line or foot, particularly in iambic meter where line starts with unstressed syllable before first stressed beat. Upbeat creates rising rhythm and forward momentum as line moves toward stress. The term borrowed from music emphasizes poetry's rhythmic nature and connection to musical patterns. Understanding upbeat helps readers perceive metrical structure and rhythmic movement, recognizing how lines build toward stress through preliminary unstressed syllables that create anticipation and momentum.

Upbeat consists of unstressed syllable(s) beginning a line or phrase before the first stress. This anacrusis provides rhythmic lead-in, creating natural flow into the metrical pattern.