A math teacher would say that lines consist of only one dimension, length. In the real world, creating art through a one dimensional line would not be practical. A more usable definition might be that line is the path of a dot, point etc. through space and that is always has more length than thickness. Lines are not all the same, especially in art.
Types of Lines
Vertical lines: are straight up and down and perpendicular to horizontal lines
Horizontal lines: are straight up and down and perpendicular to vertical lines
Diagonal lines: are lines that straight in any direction except vertical or horizontal
Zigzag lines: are a series of diagonal lines joined end to end
Curved lines: are lines that bend in any amount of degree; they may be gently wavy to tightly wound spirals
Variations of Lines
Lines come in many varieties. They may:
be long, short or anything in between
be thick, thin
be smooth or rough
be continuous, implied, dotted, dashed
change direction
change in degree of curve (curved Lines)
be any of the above combined
Some ways Artists use line
to outline; a starting place for many drawings or paintings
to suggest moods or emotion; lines can appear calm, nervous, angry, etc.
to lead the viewer\’s eye through a work of art
to create lightness or darkness; lines placed close together appear darker than those placed further from each other
to create texture; roughness or smoothness
Common types of line drawings
contour line drawing; drawings that use a fairly continuous line to represent the edges and surface detail of shape or objects being drawn
gestural line drawing; drawings that use quick pencil strokes (or other drawing instruments) to capture a scene. gestural drawings imply action and movement
hatched and cross hatched line drawing; drawings that consist of parallel lines (hatching) or crossing parallel lines (cross-hatching) drawn to create changes in lightness and darkness and texture.