Line
A directional trace that defines movement, a boundary, or continuity between points.
In practice
A line is a trace with direction. It can describe a boundary, such as the outline of a shape; connect points, as on a route map; or suggest movement, as a sweeping curve does. Its character, thick or thin, straight or wobbly, also carries feeling. On a subway map, thick colored lines show routes and thin gray lines mark districts, so line weight alone sorts what matters.
Try this
Draw ten lines that express ten words, such as calm, angry and tired, using only shape and thickness.