I had written a small bit on Reverse Arb and SLB a while back, here is the link.
Reverse arbitrage is the strategy you can take when futures price is at a discount to the underlying stock price. So if Reliance Futures is at 880 and stock price is at 900 (futures at a discount), the strategy you take to make this arbitrage difference (ideally futures should be at a premium) of Rs 20 is called a reverse arb.
How you take this strategy would be to Short Reliance stock (250 or multiples of it as 1 lot = 250) at Rs 900 and at the same time buy reliance futures at 880. On the expiry day when price of both the stock and future would be the same, reverse this trade to make risk free profit of Rs 20 (Rs 5000/lot).
The issue with this though is that to short Reliance stock and hold it till the expiry you either need to have reliance stock in your demat account or borrow it from someone else. This mechanism where you can borrow stocks is called SLB (stock lending and borrowing). SLB is still not very popular, but will definitely improve when stock options will move away from being cash settled to actual delivery of the underlying like in developed markets. So SLB presently in India is still in early stages...