II. Formation of Contracts, G. Mistake, Fraud, Misrepresentation, Duress, and Undue Influence, 1. Mistake, § 197 - Definition and nature of mistake, generally
In general, a mistake can be defined as a belief that is not in accord with the facts, and it has been specified that the term "mistake" refers to the party's beliefs at the time the contract is made, not the party's acts. However, "mistake" in a contract has also been defined as an unintentional act or omission arising from ignorance, surprise, or misplaced confidence, which is so substantial and fundamental as to defeat the object of the parties.
Reformation may be granted to correct an erroneous instrument to express the true intent of the parties to the instrument.