An e-paper display on an eBook reader allows you to read in sunlight without the image appearing to fade. Conventional backlit displays such as those on a PC or tablet emit light but electronic paper displays reflect light like ordinary paper. This makes it theoretically more comfortable to read and makes it possible to read the screen in bright situations.
If you plan to be reading your eBooks on the beach or in the sun you may be better off purchasing a dedicated eBook reader with an e-paper display rather than a tablet – or even as well as a tablet if you are feeling flush with funds. There are some other advantages to e-paper - the battery life of the reader between recharges is much, much greater and the purchase price is usually significantly less.
Want to know how it the technology works? E Ink Corporation is one the world's largest suppliers of displays to the eBook industry. Follow this link to their technology page to read an explanation.