Stuff written by somebody else that you can modify and publish as your own. I googled and found this. No idea if that's reliable source or anything - so I'm not recommending them - just something I saw when typed "PLR articles" in google.
Private label rights is a concept similar to reselling, but the merchant is permitted to modify the product to fit his or her needs. Typical PLR products are articles, reports, eBooks, and autoresponders. This kind of content is used for the purpose of allowing multiple buyers to invest in the content with free rein to alter and use it by claiming authorship of it. It is typically used in online affiliate marketing systems. http://en.wikipedia.org/wiki/Private_label_rights
Its basically an e-book written by an individual , who allows you to buy there product and resell it! You can even edit some book in your won words and mix it up if you chose too! You can Google keyword such as resell e book etc to get some nice sites!