**The main types of lines are horizontal lines, vertical lines, perpendicular lines and parallel lines.** Other categories of lines include diagonal lines, curved lines, contour lines and continuous lines.

Five types of lines are typically used in geometry:

- Vertical lines run straight up and down and have an undefined slope.
- Horizontal lines run straight across and have a slope of zero.
- Perpendicular lines intersect each other at a 90-degree angle. They occur when horizontal and vertical lines meet.
- Parallel lines are two straight lines that never intersect.
- Skew lines are special lines that exist in three or more dimensions and are nonparallel lines that never intersect.

Two types of lines are typically used in drawing:

- A contour line is a single line that creates the outline of a figure and shows height and width.
- Continuous lines in drawing are created when an image is drawn using only one line.