Assume you are long on Nifty Futures @ 7600 expiring 26th June 2014 with an expectation that the futures will hit 7900. On 26th June this does not happen…but your are still convinced that the futures will hit 7900. So on 26th June you will close June contract and buy July contract expiring on 31st July hoping 7900 will happen sooner or later.
So what you have done is essentially a rollover of position.