From entry efficiency in glossary Human Computer Interaction the Basics
Efficiency is one of the three core components (effectiveness, efficiency and satisfaction) in ISO 9241, which are widely regarded as key criteria for effective user interface design. Efficiency is concered with how easy or effortful it is for users to perform a task with a system. For example, in a library system, can the librarian or library user simply scan a barcode, or do they need to manually enter details of the book?
Efficiency often involves more-or-less measures such as time to complete task or pecentage or number of errors. It may also include cognitive measures such as working memory requirements or other forms of cognitive load.