The EPUB (Electronic Publication) format is a widely used, open-standard ebook format optimized for reflowable text. This means the text adapts to the screen size and orientation of the reading device, providing a comfortable reading experience on various devices, from smartphones and tablets to dedicated e-readers and computers. EPUB files are essentially ZIP archives containing XHTML (or DTBook) documents for the text content, CSS stylesheets for formatting, images, and metadata describing the book (title, author, publisher, etc.). The format supports features like embedded fonts, vector graphics, and interactive elements, making it a versatile choice for distributing ebooks. EPUB is designed to be accessible, allowing for features like text-to-speech and adjustable font sizes to cater to readers with disabilities. The open nature of the format has led to widespread adoption by publishers, retailers, and libraries, making it a dominant format in the ebook market. It is designed to be a single file format that can be used across multiple devices and platforms, unlike some older formats that were tied to specific devices or software.