E-book

An e-book is an e-text that forms the digital media equivalent of a conventional printed book, often protected with a digital rights management system. E-books are usually read on personal computers or smart phones, or on dedicated hardware devices known as e-book readers or e-book devices. Many mobile phones can also be used to read e-books. 

Early e-books were generally written for specialty areas and a limited audience, meant to be read only by small and devoted interest groups. The scope of the subject matter of these e-books included technical manuals for hardware, manufacturing techniques, and other subjects. E-books continued to gain in their own underground markets.

Numerous e-book formats emerged and proliferated, some supported by major software companies such as Adobe's PDF format, and others supported by independent and open-source programmers. Multiple readers naturally followed multiple formats, most of them specializing in only one format, and thereby fragmenting the e-book market even more.

E-book readers may be specifically designed for that purpose, or intended for other purposes as well. The term is restricted to hardware devices, not software programs. Specialized devices have the advantage of doing one thing well readers naturally. Specifically, they tend to have the right screen size, battery lifespan, lighting and weight.