\begin{definition}[Definition:Jump Discontinuity/Jump]
Let $X$ be an open subset of $\R$.
Let $f: X \to Y$ be a real function.
Let $f$ be discontinuous at some point $c \in X$ such that $c$ is a '''jump discontinuity''' of $f$.
The '''jump''' at $c$ is defined as:
:$\ds \lim_{x \mathop \to c^+} \map f x - \lim_{x \mathop \to c^-} \map f x$
\end{definition}