ePub (short for electronic publication; alternatively capitalized as 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. 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.
Portable Document Format (PDF) is a file format created by Adobe Systems in 1993 for document exchange. PDF is used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system.
HTML, which stands for HyperText Markup Language, is the predominant markup language for web pages.
FictionBook is an open XML-based e-book format, which originated and gained popularity in Russia. It is supported by e-book readers such as FBReader, AlReader, Haali Reader and Okular under Linux. The FictionBook files have the .fb2 filename extension.
The TXT file type is primarily associated with "Text File"
These are image files which can be viewed on the Cybook in grayscale (book covers etc).