When two straight lines intersect, if the included angle is 90, that is, a right angle is formed, then the two straight lines are perpendicular to each other. In this case, you can use ⊥ to indicate that a straight line is perpendicular to another straight line. For example, if the line segment AB is perpendicular to the line segment CD, you can write AB⊥CD.

More generally, "x⊥y" means that the vector X is perpendicular to the vector Y, or more accurately, X and Y are orthogonal. If two line segments or straight lines l and m are perpendicular to n, they can also be written as l⊥m and m⊥n, and if l and m are perpendicular to n, they can also be written as l ∨ n.