Accuracy and completeness with which users achieve specified goals

Standard: ISO 9241-18: Ergonomics of human-system interaction — Part 11: Usability: Definitions and concepts [ISO Standard]

The degree to which objectives are achieved and the extent to which targeted problems are solved. In contrast to efficiency, effectiveness is determined without reference to costs and, whereas efficiency means "doing the thing right," effectiveness means "doing the right thing."

Website: BusinessDirectory, Online: http://www.businessdictionary.com/definition/effectiveness.html, last visit 03.09.2019 [Business Dictionary]