What is Usability?

The ISO 9241 defines usability as
"The effectiveness (accuracy and completeness to reach a goal), efficiency (resources expended), and satisfaction (comfort and acceptability to users) with which specified users achieve specified goals in particular environments".

Usability promotes three basic principles:

• Learnability: The ease with which new users can begin effective interaction and achieve maximal performance.

• Flexibility: The multiplicity of ways the user and system exchange information.

• Robustness: The level of support provided to the user in determining successful achievement and assessment of goals