or orthographic, adj. 1. perpendicular; sometimes written ⊥. 2. A set of elements in an inner product space is orthogonal if the inner product of every pair of distinct elements is zero. One set of vectors in an inner product space is said to be orthogonal to another set if the inner product of every vector in the first set with every vector of the second set is zero. An orthogonal set in which the inner product of each element with itelf is one is said to be orthonormal.