Let , ,  be subspaces of . The subspace  for all  is called the orthogonal companion of , and  is the isotropic part of . If ,  is called non-degenerate; otherwise it is degenerate.
Let , ,  be subspaces of . The subspace  for all  is referred to as the orthogonal complement of , and  is known as the isotropic component of . If ,  is termed non-degenerate; otherwise it is degenerate.