Mistake of fact.
(f) Mistake of fact. Mistake of fact means an action based upon a belief by a person that the material facts are other than they really are; it can be that a fact exists but is unknown to the person, or that he believes something is a fact when in reality it is not. An action is not a mistake of fact if the erroneous belief is caused by the neglect of a legal duty.
19 CFR § 162.71
When used in this subpart, the following terms shall have the meanings indicated: