Designing for the largest audience possible regardless of disability or ability to speak the native language. This is a process rather than an end in itself.
Usability
Usability is the art and science of designing systems or products that are effective, efficient, engaging, error tolerant and easy to learn. Usability and accessibility are often confused. Some believe that a usable site is accessible and vice versa. The two are not exclusive, but it is important to understand the difference. Usability means that a Web site is intuitive and easy to use. Accessibility means a Web site is as barrier-free as possible. Accessibility and usability are closely related, as they both improve satisfaction, effectiveness, and efficiency of the generic user population. But while accessibility is aimed at making the website open to a much wider user population, usability is aimed at making the target population of the website happier, more efficient, more effective.
Usability Lab
A usability lab is a facility specifically for user testing. It can be portable or fixed and may vary widely in how it is equipped. It is usually a quiet room with computer equipment and a place for an observer to sit, along with a special observation area (possibly behind a one-way mirror), and equipment for videotaping. Computers in a usability lab are also often set up with logging software to capture user keystrokes and mouse movements and with scan converters, used to videotape computer screens.
Usability Testing
Usability testing is the process of carrying out experiments to find out specific information about a design. It is part three of the "Usability Evaluation Toolbox". In usability testing, representative users work on typical tasks using the website (or a prototype) and the evaluators use the results to see how the user interface supports the users in doing their tasks.
User Agent
Software to access Web content, including desktop graphical browsers, text browsers, voice browsers, mobile phones, multimedia players, plug-ins, and some software assistive technologies used in conjunction with browsers such as screen readers, screen magnifiers, and voice recognition software. Browsers are a subset of user agents. All browsers are user agents, but not all user agents are browsers.
User Interface Markup Language (UIML)
Unlike many markup languages, UMIL is not used to describe documents, rather it is used to describe elements on the page such as buttons, menu lists, and other page elements generally used in graphical user interfaces. It is used to define their placement on the page, and the actions to be taken when certain events such as mouse clicks, or keystrokes occur.
