Delta is the ratio that compares the change in price of an option to a corresponding change in the stock.
It's easier to understand this way. Look at the image below of DAL stock. The price of the stock is $24.04. The delta of the $24 call is .56. This means that for a $1.00 change in the price of DAL stock, the price of the call option will change by $0.56. This is a rough estimate, as there will be a number of factors that determine the true price of the option, but the delta will get you in the ballpark. If the price of DAL went up to $24.54, then the price of the call option would go up .28 cents (.50 x .56).
The delta of the put is .44, so if the price of the stock went down/up $1.00, the price of the option would go up/down .44 cents.
By combining delta with your projected stop and target prices of the stock, you can calculate the risk and reward for the option trade.