Unilateral mistake
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
A mistake or misunderstanding as to the terms or effect of a contract, made or entertained by one of the parties to it but not by the other.
Green v. Stone, 54 N. J. Eq. 387, 34 Atl. 1099, 55 Am. St. Rep. 577.