eBooks are a digital version of your book which can be available on every computer or laptop and most mobile devices such as a tablet, mobile phone, PDA etc. eBooks are downloaded as a certain file that needs to be opened in the correct program such as a .mobi file which is available on Kindle readers and available through the Amazon Kindle store, .ibooks which is available on Apple devices and through the iBooks store, .epub which is a standard format that can be read by the above devices, Nook reader and many more.
eBooks normally have a lower publishing cost due to the easier standardised formatting and design of a single front cover image. Although eBooks are generally cheaper they are by no means inferior to other book formats. They are growing in popularity every year and in 2013 86% of books sold (top 2500 Amazon bestsellers) were eBooks.