Usability is a term used to denote the ease with which people can employ a particular tool or other human-made object in order to achieve a particular goal. The primary notion of usability is that an object designed with a generalized users' psychology and physiology in mind is, for example: More efficient to use; it takes less time to accomplish a particular task, Easier to learn; operation can be learned by observing the object, More satisfying to use.

The method called "contextual inquiry" does this in the naturally occurring context of the users own environment. The term user friendly is often used as a synonym for usable, though it may also refer to accessibility. Usability is also very important in website development. "Studies of user behavior on the Web find a low tolerance for difficult designs or slow sites. People don't want to wait. And they don't want to learn how to use a home page. There's no such thing as a training class or a manual for a Web site. People have to be able to grasp the functioning of the site immediately after scanning the home page—for a few seconds at most.

Usability is a qualitative 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.

Any system that is designed for people should be easy to use, easy to learn, and useful for the users. Therefore, when designing for usability, 3 principles of design should be followed: Early focus on users and tasks, Empirical Measurement, and Iterative Design.