Proceleusmaticus is a metrical foot made up of four short syllables in classical quantitative verse, or four unstressed syllables in accentual-syllabic reading. It is also called a proceleusmatic. Because the foot is built from very light beats, it is rare in regular English poetry and more often discussed in classical prosody.
Example
the a-bove us and a-round us
murmured softly in the dark