Orthogonal Basis

A Basis of vectors ${\bf x}$ which satisfy

$$x_j x_k = C_{jk}\delta_{jk}$$

$$x^\mu x_\nu = C_\nu^\mu\delta_\nu^\mu,$$

where $C_{jk}$, $C_\nu^\mu$ are constants (not necessarily equal to 1) and $\delta_{jk}$ is the Kronecker Delta.

See also Basis, Orthonormal Basis