Scar tissue is made of collagen fibers, just like the rest of your skin. The main difference lies in how these fibers are arranged. Scar tissue has a look and feel that is thicker than the rest of your skin because the collagen is produced as a disorderly mass of fibers.
A pre-order is an order placed for an item which has not yet been released. The idea for pre-orders came when people found it hard to get popular items in stores due to their popularity. Companies then had the idea to allow customers to reserve their own personal copy, before the release, which has been a huge success.
Backordered: This means that the company would normally have that item but it is not in stock (they don't have it on the shelf so they can't send it to you) but they have organized that the manufactorer will deliver certain amounts of that item to them on a regular basis, so when the next shipment arrives then the company will fill your order and send it to you.