Resell rights are relatively new to most mortals, even if it's been brewing since the early 90s.

Here's a rundown of the different resale rights:

Basic Resell Rights
You've just bought a digital product - say an e-book - from someone. You have the right to resell the e-book to your customer, but your customer cannot resell it to another. You keep 100% of the profit each time you resell the product.

Resell Rights
Resell rights allow you to resell a product in either its physical or digital form. If it is a digital product, you get to pocket 100% of the profits and still enjoy the product, because digital products can usually be duplicated.

Master Resale Rights (Master Resell Rights)
Master resale rights enable you to resell the product to your customers along with the basic resell rights that come with it. Your customer in turn can also resell the product to their own customers. Master Resale Rights can be sold with the product or sold separately.

Private Label Rights
We like to call these rights the rights of "substance." Private label rights (PLR) allow you not only to buy the product but also change the product in any manner you see fit. There's more: you can change or alter the product even if it's just the title or first and second paragraphs of the e-book, and then put your name as the author.
Let's be careful with PLRs: they do not automatically confer copyright, just read the license before editing any.

Give Away Rights
These allow you to give the product away for free but you cannot resell the product or change/edit it. You're giving it away for free to improve traffic to your site and boost sales.

That's it for now, I hope this sheds some light on resell rights, and help those who are new to this industry.