\begin{definition}[Definition:Complete Measure Space]
Let $\struct {X, \Sigma, \mu}$ be a measure space.
Let the family of $\mu$-null sets $\NN_\mu$ satisfy the condition:
:$\forall N \in \NN_\mu: \forall M \subseteq N: M \in \NN_\mu$
That is, any subset of a $\mu$-null set is again a $\mu$-null set.
Then $\struct {X, \Sigma, \mu}$ is said to be a '''complete measure space'''.
\end{definition}