What Is Usability?

"The term "usable" means more than just easy to learn. Ease of learning is an important component of usability, but it is the least important of three components. To be usable, the product also has to be quick to use and relatively error-free. Most importantly, you must do what the user wants... Usability refers to three different components: the product does what you need it to do, it does that quickly and safely, and, last, it is easy to learn..."
- From the book by Jeff Johnson "GUI Bloopers"