Vertical
A vertical line is one which runs up and down the page.

In geometry, a vertical line is one which runs from up and down the page. Its cousin is the horizontal line which runs left to right across the page. A vertical line is perpendicular to a horizontal line.
See perpendicular lines.

Vertical angles

Vertical angles are different use of the word 'vertical'. Vertical angles are angles that share a common vertex and need not be drawn one above the other. See Vertical angles.

Coordinate geometry

A line will be vertical if any two points on the line have the same x-coordinate.
See Vertical line (coordinate geometry).

Other line topics