In this video the instructor talks about parallel and perpendicular lines. Parallel lines are lines whose slope is the same. Now take the equations of a couple of parallel lines. Graph those lines on a coordinate axes and you can see that the lines are parallel to each other and never intersect each other. Perpendicular lines are those whose product of slopes is negative one. Perpendicular lines intersect each other and they make a perfect 90 degrees with each other at the point of intersection. Multiplying the slopes of the perpendicular lines gives -1. Now the instructor shows examples of perpendicular lines by graphing them. This video shows parallel and perpendicular lines by graphing them using examples.