The document defines line as an element of art that is used to define shapes, contours, and outlines. It also suggests mass and volume. There are different types of lines including gesture lines, contour lines, sketch lines, calligraphic lines, and implied lines. Lines have characteristics such as width, length, direction, focus, and feeling. Horizontal lines suggest rest, vertical lines suggest loftiness, and diagonal lines imply movement. Combinations of horizontal and vertical lines communicate stability.