User centered design
A product is usable if the intended users can achieve their goals with effectiveness, efficiency and satisfaction in a specified context of use . Usability is achieved by taking a user-centered approach to design, and thus ensuring that the product incorporates characteristics that support usability.
Usability was adopted as a technical term to replace the phrase “user friendly,” which by the early 1980s had acquired undesirably vague and subjective connotations. It is a goal for product design in the scientific fields of HCI, human factors and ergonomics. In 1985 Gould and Lewis  described the central principles of what became known as user-centered design : (i) early focus on users and tasks., (ii) empirical measurement, (iii) iterative design.
Usability has since grown into an established discipline with the Usability Professionals Association founded in 1991, and the landmark book by Nielsen on Usability...
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