A portable device designed primarily for reading e-books.
E-readers are similar to tablet computers, and can be seen as a specialized type of tablet.
The features of an e-reader that make it superior for reading are a display suited for reading in any type of light (typically an E Ink display), a very long battery life, and built-in software for acquiring, organizing, and reading e-books.
Some e-readers have additional capabilities, such as a web browser. However, these add-ons are normally kept to a minimum so that the e-reader can be priced significantly lower than a full-featured tablet computer.