My guess is that it's PMD/corrosion, so it's the equivalent of a plating bubble. Probably not worth much.
On e-bay, anywhere from $0.50 to $50,000 depending on how you hype it. Actual value, a buck or so to someone who is interested.
No. It's a penny made of steel coated with Zinc! That straight line is nothing more than a zinc bubble in a straight line.