Bombay Stock Exchange Sensitive Index. A value-weighted stock market index, which tracks the performance of the 30 largest stocks on the Bombay Stock Exchange. The 30 stocks are chosen at random times, whenever the market has significantly changed enough to warrant the changes, and are chosen by the value of their free float shares. Although the index only tracks a very small percentage of the total stocks traded on the BSE, the index typically comprises about one fifth of the market capitalization of the entire stock exchange.