An Etymological Dictionary of Astronomy and Astrophysics

1. The property of → orthogonal functions.
   

2. The following conditions satisfied by the → Fourier series:
   ∫ cos (mx) sin (nx) dx = 0 (summed from -π to +π) for all m, n
   ∫ cos (mx) cos (nx) dx = 0 (summed from -π to +π) for all m ≠ n, = 2π for m = n = 0, = π for (m = n) > 0
   ∫ sin (mx) sin (nx) dx = 0 (summed from -π to +π) for m ≠ n, = π for (m = n) > 0.

See also: → orthogonal; → -ity.