载体 (zàitǐ) is a formal, technical noun meaning 'carrier' or 'medium' — it refers to something that physically or metaphorically carries, transmits, or conveys something else (e.g., a drug, a disease, culture). Unlike 媒介 (méijiè), which emphasizes the medium of communication or transmission between parties, 载体 focuses on the thing that bears or holds the content. It is not a general word for 'vehicle' like 车 or 车辆.