Open Archives Initiative. Trade and Standards Organization for the Digital Publishing Industry. EPUB. EPUB (short for electronic publication; sometimes styled ePub) is a free and open e-book standard by the International Digital Publishing Forum (IDPF).
Files have the extension .epub. EPUB is designed for reflowable content, meaning that an EPUB reader can optimize text for a particular display device. EPUB also supports fixed-layout content. The format is intended as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale.