EPUB (short for electronic publication; alternatively capitalized as ePub, ePUB, EPub, or epub, with "EPUB" preferred by the vendor) 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 the text display can be optimized for the particular display device used by the reader of the EPUB-formatted book. The format is meant to function as a single format that publishers and conversion houses can use in-house, as well as for distribution and sale. It supersedes the Open eBook standard.
EPUB became an official standard of the International Digital Publishing Forum (IDPF) in September 2007, superseding the older Open eBook standard.
In August 2009, the IDPF announced that they would begin work on maintenance tasks of the EPUB standard. Two broad objectives were defined by this working group: "One set of activities governs maintenance of the current EPUB Standards (i.e. OCF, OPF, and OPS), while another set of activities addresses the need to keep the Standards current and up-to-date." The working group was expected to be active through 2010, publishing updated standards throughout its lifetime. On April 6, 2010, it was announced that this working group would complete their update in April 2010. The result was to be a minor revision to EPUB 2.0.1 which "corrects errors and inconsistencies and does not change functionality". On July 2, 2010, drafts of the version 2.0.1 standards appeared on the IDPF website.
On April 6, 2010, it was announced that a working group would be formed to revise the EPUB specification In the working group's charter draft, 14 main problems with EPUB are identified which the group will address. The group is chartered through May 2011, and is scheduled to submit a final draft on May 15, 2011. An initial Editors Draft for EPUB3 was published on November 12, 2010, and the first public draft was published on February 15, 2011. On May 23, 2011, the IDPF released its proposed specification for final review.Source :