Perpendicular lines are two lines that intersect at a right angle, which measures 90 degrees. This relationship is often represented in geometry and is essential for various applications, such as construction and design. When two lines are perpendicular, they create four right angles at the point of intersection. In a coordinate plane, if one line has a slope of m, the slope of a line that is perpendicular to it will be the negative reciprocal, or -1/m. Understanding perpendicular lines is crucial in fields like mathematics, engineering, and architecture, where precise angles are necessary for stability and aesthetics.