There are pairs of lines that have relationships to each other that are useful to know. Perpendicular lines are at a $90\degree$ angle to each other. Parallel lines never touch and stay the same distance away from each other.

Perpendicular lines

When a line meets another at an angle of $90\degree$, the lines are perpendicular. Examples of perpendicular lines are the corners of a piece of paper.

Parallel lines

When two lines stay the same distance apart and never touch, they are parallel. A pair of train tracks are parallel lines, for example.

Example 1

Are these lines perpendicular or parallel to each other?

These lines touch so they cannot be parallel lines.