Noun
(countable, mathematics) A subset of a space which is a space in its own right.
(uncountable, science fiction) Any (often unspecified) method of communicating or travelling faster than light speed.
(uncountable, science fiction) An alternative dimension or universe, access to or use of which permits faster-than-light travel or communications; hyperspace.
subspace (uncountable)
English Wikipedia has an article on:Subspace (BDSM)Wikipedia
(BDSM) The psychological state of the submissive or "bottom" during sadomasochistic activity.
A basis for a subspace S is a set of linearly independent vectors whose span is S. The number of elements in a basis is always equal to the geometric dimension of the subspace. Source: Internet
A Banach space can be canonically identified with a subspace of its bidual, which is the dual of its dual space. Source: Internet
A nonempty subset W of a vector space V that is closed under addition and scalar multiplication (and therefore contains the 0-vector of V) is called a linear subspace of V, or simply a subspace of V, when the ambient space is unambiguously a vector space. Source: Internet
A linear subspace of dimension 2 is a vector plane. Source: Internet
A linear subspace that contains all elements but one of a basis of the ambient space is a vector hyperplane. Source: Internet
Also every subspace of a separable metric space is separable. Source: Internet