\begin{definition}[Definition:Quadratic Residue/Non-Residue]
Let $p$ be an odd prime.
Let $a \in \Z$ be an integer such that $a \not \equiv 0 \pmod p$.
If there is no such integer $x$ such that $x^2 \equiv a \pmod p$, then $a$ is a '''quadratic non-residue of $p$'''.
Category:Definitions/Number Theory
\end{definition}