Can someone please tell me what this means?
It means that if you already own one or more of the resources in a bundle, you receive a discount on that bundle.
So if you had a bundle containing three books, and you already owned one book, you'd probably get a Dynamic Pricing Discount of about 33%, depending on the length and value of each individual book relevant to the others. Dynamic Pricing is meant to prevent Faithlife's customers from having to pay for the same resource twice.