Orthogonal

In mathematics, orthogonal is synonymous with perpendicular; it means at right angles. It comes from the Greek "ortho", meaning "right" and "gonia", meaning "angle". Two streets that cross each other at a right angle are orthogonal to each other. Two vectors in an inner product space are orthogonal if their inner product is zero. The word normal is sometimes also used for this concept by mathematicians, although that word is rather overburdened.

For example, in a 2- or 3-dimensional Euclidean space, two vectors are orthogonal if their dot product is zero, i.e., they make an angle of 90 degree. Hence orthogonality is a generalization of the concept of perpendicular.

Several vectors are called pairwise orthogonal if any two of them are orthogonal. They are said to be orthonormal if they are all unit vectors. Non-zero pairwise orthogonal vectors are always linearly independent.

In computer science, an instruction set is said to be orthogonal if any instruction can use any register in any addressing mode.