An Etymological Dictionary of Astronomy and Astrophysics

A real vector space of dimension n having a symmetric bilinear form (x, y) such that in some basis e₁, …, e_n, the quadratic form (x²) takes the form x₁² + … + x_{n - 1}² - x_n². Such bases are called orthonormal.

See also: → pseudo-; → Euclidean; → space.