Orthogonality

triangle in which one angle is a 90-degree angle

90° angle (π/2 radians): an angle that bisects the angle formed by two halves of a straight line

class=skin-invert-image|right|thumb|236px|The segment AB is perpendicular to the segment CD because the two angles it creates (indicated in orange and blue) are each 90 degrees. The segment AB can be called the perpendicular from A to the segment CD, using "perpendicular" as a noun. The point B is called the foot of the perpendicular from A to segment CD, or simply, the foot of A on CD.

right-angled hexahedron, like a cube but with edges not necessarily equal in length

in geometry, an object that is perpendicular to a given object, vector perpendicular to a curve or surface

Orthogonality is a term with various meanings depending on the context.thumb|The line segments AB and CD are perpendicular to each other.