From the user's perspective, usability is an important quality factor. A usable system provides solutions for the user's problems (in other words, it has the features that the user needs) and, moreover, it solves the problems in the right way (it is easy to use). Human-centred designers study users and their needs and expectations so that the user's perscpective can guide the design of the system.

Usability is composed of several factors. For example, the ISO (International Organization for Standardization) defines usability as "the effectiveness, efficiency and satisfaction with which specified users can achieve specified goals in particular environments". ISO-9241-11. 1998. Ergonomic requirements for office work with visual display terminals (VTDs) - Part 11. Guidance on usability.

  • Effectiveness indicates whether the system includes the right features from the user's point of view.

  • Efficiency determines how quick and easy it is to use the system.

  • Satisfaction relates to how pleasant it is to use the system, how satisfied the user is with the using the system, and how the user feels about the product.

For consumer and entertainment applications, the definition of usability often expands to questions such as how easy it is to learn to use the system, how rich it is in experiences, and how much trust the user has in the technology. Usability cannot be defined in absolute terms, it always depends on the users, the users' goals and the environment of use.

Usability research also investigates the usefulness and acceptability of products. Technology acceptance models aim to predict the acceptability of technical solutions, i.e. the readiness of people to take technology into use.