Cognitive Disabilities and the Web: Where Accessibility and Usability Meet?
Additional definitions of usability
"Usability is the extent to which users can access the functionality of a system with effectiveness, efficiency, and satisfaction to achieve specific goals. Employing user/human-centered design processes helps ensure that products or systems are highly usable and meet users' needs. These processes emphasize and utilize the user perspective throughout design, development, and test" (7).
"Usability means that the people who use a product can do so quickly and easily to accomplish their own tasks" (6)
"Usability means making products and systems easier to use, and matching them more closely to user needs and requirements" (33).
"Usability is the measure of the quality of a user's experience when interacting with a product or system — whether a Web site, a software application, mobile technology, or any user-operated device" (34).