According to ISO 9241(Ergonomic Requirements for Office Work with Visual Display Terminals), usability is "the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use". Therefore, web usability can be defined as the ability of Web applications to support web-related tasks with effectiveness, efficiency and satisfaction. Effectiveness represents accuracy and completeness when users achieve a specified goal. Efficiency is resource cost in relation to the accuracy and completeness. Satisfaction is the comfort and acceptability of use.