Just like 2 Stock Exchanges NYSE and NASDAQ in USA , similarly, in India, we have Bombay Stock Exchange (BSE) and National Stock Exchange (NSE).
SENSEX and NIFTY are the index of BSE and NSE respectively that calculate the rise and fall of the Stock Market.
SENSEX & NIFTY are the barometer of the Stock Market Movement.
Just as Dow Jones is a bunch of top 30 companies of NYSE and NASDAQ in USA ,SENSEX is a bunch of top 30 shares and NIFTY is a bunch of a top 50 shares of Indian Stock Market. Through these two indexes, one can keep a check on the economic health of the Indian Economy.