What is "null set"

n. 1 (context mathematics measure theory English) A negligible set; set of zero measure. 2 (context set theory English) The empty set.

n. a set that is empty; a set with no members

In set theory, a null set N ⊂ R is a set that can be covered by a countable union of intervals of arbitrarily small total length. The notion of null set in set theory anticipates the development of Lebesgue measure since a null set necessarily has measure zero.