Perpendicularity refers to the relationship between two lines, segments, or planes that intersect at a right angle, which is 90 degrees. In geometry, this concept is essential for defining shapes and structures, ensuring that elements are aligned correctly. For example, the edges of a square or rectangle are perpendicular to each other. In practical applications, perpendicularity is crucial in fields like engineering and architecture. It ensures that components fit together properly and that buildings are stable. Tools like the carpenter's square are often used to check for perpendicularity, helping to maintain accuracy in construction and design.