\begin{definition}[Definition:Proper Morphism of Schemes]
Let $\struct {X, \OO_X}$ and $\struct {Y, \OO_Y}$ be schemes.
Let $f : \struct {X, \OO_X} \to \struct {Y, \OO_Y}$ be a morphism of schemes.
$f$ is '''proper''' {{iff}} $f$ is separated, of finite type and universally closed.
\end{definition}