The document defines and describes different types of lines used in art. It states that a line is a mark made by a moving point and can be either simple, consisting of a single line, or composite, consisting of two or more lines. Composite lines are further broken down into zig-zag lines made of straight line fragments, wavy lines made of curved fragments, and mixed lines with both straight and curved fragments. The document also explains that different line directions like horizontal, vertical, and diagonal can communicate feelings like rest, loftiness, and movement respectively.