Original Cost

For a Position, it is the quantity-weighted price of the Transactions opened on the first day of the Position. Simply put, it's your original trade price of the package that you'd see when entering the order in your trading platform.

Often times people like to calculate their profit target/loss on the original trade price (basis), so this lets you quickly calculate what that would be.

For example, selling a Strangle for $1.00 and then rolling the call side for a $0.25 credit would result in an Original Cost of $1.00 and Breakeven of $1.25. If you are aiming to take 50% of your original credit, you'd know at a glance that the target should be $0.50, and then apply that to the Breakeven to get a target exit price of $0.75 ($1.25 - $0.50).