The ePub format (file extension .epub) is a standard for eBooks created by the International Digital Publishing Forum. It is the standard eBook format on Apple iOS devices, which currently include the iPad, the iPhone and the iPod Touch. Help & Manual's ePub output is designed to be fully compatible with the Apple iBooks® eBook reader on these devices so that you can distribute your ePub output through the Apple iTunes store.
In addition to Apple iBooks®, ePub is also supported by most other hardware eBook readers, including the Sony Reader series, other smartphones and many other devices, and by many software readers like the Adobe Digital Editions reader.
See ePub Resources for more details, including sources for reader software and devices.
Please note that the support for Apple iBooks®/ePub is only included in the Professional and Server versions of Help & Manual. You cannot generate iBooks®/ePub with the Basic version.