An EReader is a digital book reader
With an eReader, you can download and read digital books. It's a way to put a lot of books on 1 device, so you don't have to drag a whole suitcase with books everywhere. There are several e-readers from different manufacturers, and there are also different types of digital books. You can also read a book on your PC or mobile phone, but generally it doesn't read that pleasantly. An eReader uses e-ink (electronic paper), which makes it very much like paper and reads it pleasantly (additional advantage is also that it only consumes power when refreshing the page, and not continuous.
The big advantage of ebooks/ereaders is that you can spend a lot of books on one device. The purchase of the books is also cheaper than a paper book. The big disadvantage is the purchase price of an ereader because it is around 200 euro. In The Netherlands The ereader is put on the map by the collaboration between Bol and Sony. Other readers are the Amazon Kindle, the Nook, Irex Iliad, etc.