The document discusses the key characteristics and uses of lines in art and design. It explains that a line is formed by points that lose their individual identity and form a new entity. Lines have length and width but no depth, and are used by artists to create outlines and edges. The direction of a line can influence the mood conveyed, with horizontal lines appearing calm, vertical lines showing potential for movement, and diagonal lines strongly indicating action. Lines are a basic but important part of every shape.