Vertical lines are best described as moving in an up and down or down and up direction and are known as being “perpendicular” to the earth’s surface/horizon, or any other horizontal line.
Diagonal lines are usually described as straight lines that “slant”. It can go in any direction like left or right, but it will appear seemingly skewed or angled in that direction.
Curved lines are often described as bending in form and can be spiral-shaped or wavy. They are also attributed to aspects of “sensuality”, conveying the natural curves we see on the human body, or other aspects like fluidity or softness.
Contour lines refer to the outlines of a subject matter, which will provide the fundamental structure or shape of the object or figure in the visual composition.