The wikipedia definition is a bit abstruce. One of the links in the external links section has a much better definition, and is more relevant to usability rathe

The wikipedia definition is a bit abstruce. One of the links in the external links section has a much better definition, and is more relevant to usability rather than being the more general definition: http://www.usabilityfirst.com/glossary/term_66.txl http://www.usabilityfirst.com/glossary/term_66.txl