This is just another term for pirate DVDs: an illegal sub-standard DVD-R copy of an officially released DVD. Sometimes people will openly offer a copied (pirated) DVD for sale and state that it is legal to buy as a back-up if you already own a legitimate version, thus placing the onus on you to remain within the law (or not). Whatever they tell you and regardless of whether you and / or they own legitimate issues of the DVD in question, it's illegal for them to sell it and for you to buy it. It's just a common misinterpretation of the law that sellers of dodgy goods try to use to their advantage. Copied DVDs sold as back-ups will usually be sold in a plastic wallet without artwork or case, will often have a blank label and will be DVD-Rs of the same sort of standard as a pirate being passed off as legitimate.