Deep in the money is any option contract that has nearly all its value in intrinsic terms (difference between strike price and current price) and minimal extrinsic or time value. For eg: If Nifty is trading at 18500 and I have a call option of strike price 17500 priced at โน1050 then only the time value (extrinsic value) is only โน50 and intrinsic value is โน1000 which is nothing but difference in strike price and market price.