On Amazon, there are two ways authors can list their books. One way is to go wide, which means that you list them on Amazon but also on other online retailers. The second way is to go exclusive (or narrow), which means you enter the books into Kindle Unlimited.
If you're not familiar with Kindle Unlimited, it's a subscription service for readers. Readers pay $9.99/month (in the US), and in return, they can read as many books that are in Kindle Unlimited as they want for free. When a book is in Kindle Unlimited, though, the author cannot list it on other retailer sites. It is on Amazon only, which is why we call it exclusive.
Well, I have put my books in Kindle Unlimited to see if I can reach more readers that way. You can still buy the ebooks (or print books) in the same way, but Kindle Unlimited subscribers can now read them for free.
By the way, if you're curious about it, authors still get paid when people read their books in Kindle Unlimited. But instead of a percentage of a sale, the authors get paid by the number of pages read. It comes out to about the same amount either way.
So, if you are a Kindle Unlimited subscriber, and you have not yet read Infusion, Profusion, Savage, Blue Arrow, or Parthenium's Year, you can now get them for free!
Every human being needs a creative outlet. That's why I write.