dedekind cut

noun Mathematics.

1. two nonempty subsets of an ordered field, as the rational numbers, such that one subset is the collection of upper bounds of the second and the second is the collection of lower bounds of the first: can be used to define the real numbers in terms of the rational numbers.

noun

1. a method of according the same status to irrational and rational numbers, devised by Julius Wilhelm Dedekind (1831–1916)