\begin{definition}[Definition:Net (Metric Space)]
Let $M = \struct {A, d}$ be a metric space.
Let $\epsilon \in \R_{>0}$ be a strictly positive real number.
An '''$\epsilon$-net for $M$''' is a subset $S \subseteq A$ such that:
:$\ds A \subseteq \bigcup_{x \mathop \in S} \map {B_\epsilon} x$
where $\map {B_\epsilon} x$ denotes the open $\epsilon$-ball of $x$ in $M$.
That is, it is a subset of $A$ such that the set of all open $\epsilon$-balls of elements of that set forms a cover for $A$.
\end{definition}