duct — a tube or passage that carries air, liquid, cables, or other materials

a maintenance worker in coveralls points upward at large silver metal tubes running along the ceiling. The rectangular metal passages carry streams of air shown as flowing blue wisps moving through them. One section of the tube system branches into smaller passages that lead toward different areas. The flowing air streams split and follow each pathway as they transport fresh air throughout the building. Another worker holds a clipboard and nods while observing the efficient air movement system. tubes and passages that carry air and other materials from one place to another