Usability

Usability is the extent to which a product, system, or service can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use, as defined by ISO 9241-11. It goes beyond mere accessibility compliance to encompass the actual quality of the user experience — whether people can complete tasks successfully, do so without unnecessary effort, and feel satisfied with the interaction. In the accessibility context, ISO 9241-220 frames accessibility as usability for people with the widest range of capabilities, making usability and accessibility deeply interconnected concerns. Evaluating usability typically involves measuring task completion rates, time on task, error rates, and subjective user satisfaction.