\begin{definition}[Definition:Categorical (Model Theory)]
Let $T$ be an $\LL$-theory.
Let $\kappa$ be a cardinal.
$T$ is $\kappa$-'''categorical''' if whenever $\MM$ and $\NN$ are models of $T$ of cardinality $\kappa$, then $\MM$ and $\NN$ are isomorphic.
\end{definition}