The Nifty and the Sensex are both Indices.
The Sensex also called the BSE 30, is a stock market index of 30 well-established and financially sound companies listed on the Bombay Stock Exchange (BSE). The Nifty, similarly, is an indicator of the 50 top major companies on the National Stock Exchange (NSE).
Sensex and Nifty are both indicators of market movement. If the Sensex or Nifty goes up, it means that most of the stocks in India went up during the given period. If the Nifty goes down, this tells you that the stock price of most of the major stocks on the BSE has gone down.
Nifty Futures are a form of index futures where the underlying is the S&P CNX Nifty index. Nifty Futures Contracts have three expiration dates: the near month, mid-month, and far month. The expiration day for each contract is the last Thursday of every month. Nifty Futures are the most traded contracts in India.