**Parallel lines exist everywhere in everyday life, including on the sides of a piece of paper and the way that the shelves of a bookcase are positioned.** Parallel lines are two or more lines that when drawn out infinitely long never intersect.

For example, a rectangle or a square is made up of four sides, where the opposite sides are parallel to each other. In a trapezoid, two of the sides are parallel where as the other two are slanted towards each other and, therefore, are not. Because of the many shapes in which parallel lines can be found, they have several applications in everyday objects.

In geometry, parallel lines can be identified and drawn by using the concept of slope, or the lines inclination with respect to the x and y axis. Two lines with the same slope do not intersect and are considered parallel. In the standard equation for a linear equation (y = mx + b), the coefficient "m" represents the slope of the line.

On a standard Cartesian plane, there are infinitely many parallel lines that can be drawn with respect to one another. On the contrary, equations that intersect at a 90-degree, or right angle, are considered perpendicular.