In geometry, a hyperplane is a subspace whose dimension is one less than that of its ambient space. Wikipedia

A subspace whose dimension is one less than that of its ambient space Wikipedia Disambiguation

Geometric object Wikidata

An n-dimensional generalization of a plane; an affine subspace of dimension n − 1 that splits an n-dimensional space. (In a one-dimensional space, it is a point; in two-dimensional space it is a line; in three-dimensional space, it is an ordinary plane.). Wiktionary

An n-dimensional generalization of a plane. Wiktionary (translation)