It's a somewhat obsolete term for "lack of information" : http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-knowing http://www.av8n.com/physics/thermo/

It's a somewhat obsolete term for "lack of information" : http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-knowing http://www.av8n.com/physics/thermo/entropy.html#sec-s-not-kn... (Yes, it is indeed context-dependent.)