Hang Seng Index, theHang Seng In‧dex, the /ˌhæŋ ˈseŋ ˌɪndeks/ trademarka number that shows how well or badly shares in companies have performed on the stock exchange in Hong Kong on a particular day. The number is based on the share prices of large companies. →Dow Jones Average, FT 100 Share Index, Nikkei index