a hole (usually with a flush cover) through which a person can gain access to an underground structure
manhole详细解释
man.hole
n.（名词） A hole, usually with a cover, through which a person may enter a sewer, boiler, drain, or similar structure. 下水道出入孔：一种常带有盖的孔道，人可以由此孔进出排道、锅炉、下水管或类似设施
