Vertical lines are straight lines that run up and down, perpendicular to the horizontal lines. They are often used in art, design, and architecture to create a sense of height and stability. In mathematics, vertical lines can be represented on a graph, where they indicate a constant value of the x-coordinate. In everyday life, vertical lines can be seen in structures like buildings, trees, and poles. They help to define shapes and create visual interest. Vertical lines can also influence how we perceive space, making areas feel taller or more open.