A subset $A \subset\mathbb R^n$ has measure zero if for every $\varepsilon > 0$, there exists a countable covering of $A$ by rectangles ${Q_i}_{i\in\mathbb N}$ such that the sum of the volumes of the $Q_i$ is less than $\varepsilon$, i.e. that \(\sum_{i\in\mathbb N} \text{vol}(Q_i) < \varepsilon.\)
Wikidata ID: Q1201815