Noun
nonresidue (plural nonresidues)
(mathematics) A value that is not a residue.
An integer a is a quadratic residue modulo p if it is congruent to a perfect square modulo p and is a quadratic nonresidue modulo p otherwise. Source: Internet
A quadratic nonresidue (mod n) is any number that is not congruent to a square (mod n). Source: Internet