So, what is PLR? Basically, PLR content is GENERIC content. It's content that's bought to form the foundation of something else. People buy PLR content to launch websites, and to promote products and services. PLR content is created so that it can be edited, and transformed into something else… into whatever weird and wonderful things the buyer wants to do with it.
PLR works like this, sales-wise.
Let's say you're selling an article:
Standard article: sold with (whatever) rights to one buyer. Depending on which rights you sold the first time, you may sell it again to another buyer.
PLR article: sold with all rights to many buyers.