\begin{definition}[Definition:Normal Bundle]
Let $M$ be a differentiable manifold.
Let $p \in M$ be a point in $M$.
Let $N_p M$ be the normal space at $p$.
The '''normal bundle''' of $M$ is the disjoint union of all the normal spaces of $M$:
:$\ds N M = \coprod_{p \mathop \in M} N_p M$
\end{definition}