(Latin: ignorore, to have no knowledge of)
The state of being without knowledge; more precisely, the want of knowledge in a subject capable of possessing this knowledge.
Taking account of the person in whom ignorance exists, it is either privative or negative.
The former is ignorance properly so-called, the absence of that knowledge which one can and should have, as the lack of medical knowledge in a physician.
Negative ignorance, or nescience, is the absence of knowledge not required by one's position in life.
Ignorance is deemed invincible when it persists in spite of ordinary diligence to dispel it; it is reckoned morally vincible and culpable when it is due to the failure to utilize one's natural resources.
Ignorance which is purposely fostered is termed affected; if it is a product of sheer negligence, it is called crass or supine.
No ignorance of nullifying laws, e.g., of irregularities or impediments, excuses from their observance; if not affected, ignorance excuses from incurring penalties.
New Catholic Dictionary