the Hang Seng IndexHang Seng In·dex, the /ˌhæŋ ˈseŋ ˌɪndeks/ trademark a 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, the, Nikkei index, the