Orthogonal lines are lines that intersect at a right angle, which is 90 degrees. In geometry, this concept is important because it helps define shapes and angles. When two lines are orthogonal, they create a clear and distinct relationship, often used in various fields such as architecture and engineering. In a Cartesian coordinate system, orthogonal lines can be represented by the axes: the x-axis and the y-axis. These lines are perpendicular to each other, forming a grid that helps in plotting points and understanding spatial relationships. This property is essential in mathematics and physics for analyzing different phenomena.