There is no difference. Both are same the S&P CNX NIFTY index, commonly called as NIFTY or NIFTY 50 in TV or newspapers.
The words actually come from futures. The spot means the value of the underlying. Example: If NIFTY is trading at 5000 and NIFTY futures are trading at 5003, then you can put it as "futures are trading at a premium of 3 points compared to the spot".