In air conditioning and ventilation, conditioned air travels through passages known as ducts. These systems move heated or cooled air from an air handler to spaces and back for reprocessing. Ducts are typically constructed from sheet metal or flexible materials, with designs prioritizing minimal air leakage. Other terms like 'shaft' (vertical passage for lifts/services), 'channel' (general term, not standard HVAC nomenclature), and 'pipe' (for pressurized liquids/gases, not large air volumes) are not applicable. Therefore, 'duct' is the correct designation.