There are different types of Kindles, such as the Kindle Fire and Kindle 2. This node is about what they all have in common, and it mostly applies to Kindle apps too.
Kindles are tablet sized or smaller devices used to read e-books. They are designed to be used with mobi files, making it harder to upload e-books to servers where they can be downloaded for free. Kindles are completely integrated with Amazon's website, making purchasing and downloading e-books extremely convenient. Amazon also makes it easy for independent authors and publishers to sell e-books for lower prices than major publishing houses, and attempts to get major publishing houses to sell e-books for less than they would prefer. It is also possible to 'lend' a kindle book to someone else for fifteen days, although major publishing houses will not let this feature be activated for their books. When you lend a book to someone else it because unavailable to you for that period of time, and it is returned automatically even if the borrower 'forgets'. Even when lending is enabled, each book may only be lent once. They cannot be resold, the fine print explains that you have only bought a license for personal use.
Kindles tend to have non luminescent screens which are back lit, unlike many tablets which have luminsecent screens.