What is the definition of perpendicular lines? Perpendicular lines are two lines that share more than one common point. Perpendicular lines are two lines that share more than one common point. Perpendicular lines are two lines that intersect to form four congruent right angles. Perpendicular lines are two lines that intersect to form four congruent right angles. Perpendicular lines are two lines that cut each other in half. Perpendicular lines are two lines that cut each other in half. Perpendicular lines are two lines that never intersect.