ignorance
lack of knowledge or understanding
innumeracy
inability to basically reason about numbers, use them to perform tasks, and do arthrithmetic
rational ignorance
practice of avoiding research whose cost exceeds its benefits
functional illiteracy
reading and writing skills that are inadequate "to manage daily living and employment tasks that require reading skills beyond a basic level."
mistake of law
defense (or lack thereof) to criminal charges on the grounds of ignorance of law