In the breakdown description I received from a publisher, they mention that they also pay industry leading royalties of ##%.
What does that mean?
That is a marketing ploy that they are using to claim that they provide royalties that might be considered to be higher than the average royalties paid by other publishers. Considering that these royalties are usually pretty meager at best anyway, that probably isn't much of a claim!
As far as determining what the industry average really is, it would depend on the type of book. I believe most royalties tend to be anywhere from 7% to 17% and will vary by genre as well as whether it is for a trade paperback or hardbook, or fiction versus non-fiction.
Make sure you read the fine print, though, especially if any form of advance is being offered. If you are receiving an advance, then you will NOT receive any royalties until the publishers recover the money they paid you for the advance. Furthermore, be cautious concerning multiple books published with the same company. If they try to put all your books into a single basket, then you may find it even more difficult to retrieve any royalties. This is because they will expect to recover the advances on ALL books that are lumped together before paying royalties on ANY book.
For example, they give you a contract for three books, with a $5000 advance on each book. Book #1 earns back $2000, Book #2 earns back $3000, and Book #3 earns back $5000. If all three are lumped into the same basket, then the publisher will not pay royalties on any of the books until they get back $15,000, and in this example you have only earned $10,000. If each book is handled separately, then you would start earning royalties now on Book #3 because it has earned back the advance for that particular book.
"Industry-leading" (please note the hyphen in the compound adjective) means "they lead the industry in this." So they claim they are offering royalties which are among the best in the industry.