Integrating Usability and Accessibility  

Usability is a concept that we intuitively know when we experience it. The notion of usability can refer to ease of use, ease of learning, efficiency and usefulness. To render a satisfying user experience, a well-designed product should have a combination of these features.

Johannesen, Leila, Joe Sacco, Tim Hogan and Marc Boegner. IBM (2004). Articles>Usability>Accessibility