AZW3, also known as Kindle Format 8 (KF8), is a refined version of the AZW file format used by Amazon Kindle e-readers. It's essentially a compiled HTML format, incorporating features from both the older MOBI format and HTML5/CSS3. This allows for more advanced formatting options, including support for complex layouts, embedded fonts, and interactive elements within ebooks. AZW3 files are DRM-protected, meaning they are often tied to a specific Amazon account and device, restricting their use on unauthorized platforms. The format supports a wider range of fonts and styling compared to its predecessor, MOBI, resulting in a richer reading experience. It's the primary format used for ebooks purchased from the Amazon Kindle Store and is designed to be optimized for the Kindle ecosystem. While MOBI files can be read on Kindles, AZW3 is the preferred format for newer books due to its enhanced capabilities. The format is proprietary to Amazon, and while there are tools to convert other ebook formats to AZW3, the process may not always be perfect, especially with complex layouts.