Usability is a measure that describes how easy, effective, learnable, satisfying, and error free an application or a device is, to the average user. Usability can significantly reduce development time and costs through end-user research and testing throughout the product development life cycle.
There are many definitions for usability on the web, two of which are listed below.
"Usability is a quality attribute relating to how easy something is to use. More specifically, it refers to how quickly people can learn to use something, how efficient they are while using it, how memorable it is, how error-prone it is, and how much people like using it." (Jakob Nielsen)
"Usability really just means making sure that something works well: that a person of average (or even below average) ability and experience can use the thing whether it's a website, a fighter jet, or a revolving door for its intended purpose without getting hopelessly frustrated." (Steve Krug)
