Non-residue

of power $ n $ modulo $ m $

A number $ a $ for which the congruence $ x ^{n} \equiv a\ ( \mathop{\rm mod}\nolimits \ m) $ has no solution. See also Remainder of an integer.

Comments

Usually this term refers to the case $ n = 2 $. It was first used by C.F. Gauss in his Disquisitiones Arithmetica.