Kindle Unlimited is a subscription service offered by Amazon that allows users to access a vast library of eBooks, audiobooks, and magazines. For a monthly fee, subscribers can read or listen to as many titles as they want from the collection, which includes over a million options across various genres. With Kindle Unlimited, users can borrow books for as long as they like, but they can only have a limited number of titles checked out at once. This service is compatible with Kindle devices and the Kindle app, making it easy to enjoy reading on multiple platforms.