From Wikipedia: Usability is a term used to denote the ease with which people can employ a particular tool or other human-made object in order to achieve a particular goal. Usability can also refer to the methods of measuring usability and the study of the principles behind an object’s perceived efficiency or elegance.
This blog is about the web and web usability, yet not exclusively. Usability leads to productivity and valuable content. Usability leads to great user experience.