New: A brand-new, unused, unopened and undamaged items in original retail packaging (where packaging is applicable).
Used: Items that have been previously used. The items may have some signs of cosmetic wear, but are fully operational and functions as intended.
Refurbished: Items that have been restored to working order by the seller or a third party not approved by the manufacturer. This means the items have been inspected, cleaned and repaired to full working order and are in excellent condition. This items may or may not be in their original packaging.
Customer Returns: In general returns are items that have been ordered from the source company and have been sent back by the customer. There are many reasons as to why products have been returned. They could be faulty, the wrong color, box damaged and unwanted gift, not as described by the catalogue, parts missing. Or returned for the simple reason they have a guarantee and the customer have changed there mind. Returns are untested and unchecked raw returns and may need repair, rework or recycle for the products to be fit for resale. Or alternatively to be sold as a second hand products.
Grade A: Goods are "Factory Reconditioned" to the Manufacturers original specification. With grade A stock there is always a chance that there may be a minor cosmetic mark, considering the price however these are considered to be very minor and will not affect performance of the product.
Grade B: Stocks are raw customer returns. As such you will find a large range of conditions which will vary pallet to pallet. Within a pallet you can get items that have been smashed, damaged in transit, have parts missing or have simply been returned because they are not wanted.
Grade C: Damaged items, usually with defects that can be repaired. Incorrectly mail ordered products damaged while transporting or broken. These products are not sold under warranty.
Mixed Grages: Mix of items from B and C grades, possibly including A Grade goods. Usually, most of them work and have the original boxes unless the description of a certain offer states differently. Mixed Grages products are not tested and are not sold under warranty.
Salvage: Damaged Insurance Salvage / Damaged Cargo. Abandoned, condemned, damaged, deteriorated, discarded, incomplete, obsoleted, or worn property for recycling, refabrication, restoration, reuse, or scrapping. Items that have value in excess of its value as a scrap, but is no longer useful for its intended or original purpose.
Also, please check out this article: What exactly are refurbished products?