Introduction • Usability

Definition: Usability is a quality attribute that assesses how easy user interfaces are to use. The word "usability" also refers to methods for improving ease-of-use during the design process

Usability usually refers to software but is relevant to any product. Some ways to improve usability include shortening the time to accomplish tasks, reducing the number of mistakes made, reducing learning time and improving people's satisfaction with a system.

What Makes A Person Want To Come Back? According to Arthur Andersen (1 May 2001), the online information company, the top reasons why people revisit a site are ease of use, ease of navigation, quality of content and look and feel of the site.

Usability depends on a number of factors including how well the functionality fits user needs, how well the flow through the application fits user tasks, and how well the response of the application fits user expectations. We can learn to be better user interface designers by learning design principles and design guidelines. But even the most insightful designer can only create a highly-usable system through a process that involves getting information from people who actually use the system. Usability is the quality of a system that makes it easy to learn, easy to use, easy to remember, error tolerant, and subjectively pleasing.

Usability is one of the focuses of the field of Human-Computer Interaction. As the name suggests, usability has to do with bridging the gap between people and machines. A user interface (or human-computer interface) refers to the parts of a hardware and/or software system that allow a person to communicate with it. This includes output devices (the way the computer talks to a user) and input devices (the way a user talks to the computer). Typical "output devices" include computer monitors and the windowing systems that run on them, but also include speakers and other devices that provide feedback. "Input devices" include peripherals like keyboards, mice, and joysticks, but also include microphones and even eye movement devices. Each of these interface components has devices corresponding to the visual (sight), aural (sound), and haptic (touch) channels of the brain. Usability engineering studies these elements of the user's experience.

Usability 101: Introduction to Usability http://www.useit.com/alertbox/20030825.html
Usability First http://www.usabilityfirst.com