The term diagonal refers to a line or direction that is at an angle of 45 degrees to two other lines, creating a right triangle. It can also refer to something that cuts across or spans in a diagonal manner, such as a diagonal pattern on a piece of clothing or the diagonally-shaped space between two buildings. In mathematics and geometry, the term is used to describe a vector or matrix with elements that form an angle of 45 degrees to its rows or columns.