The term "abstract art" is like the term "modern music" in the sense that it is a very broad umbrella sheltering a wide variety of art. But like "abstract math," the general sense of the term is that it is the opposite of the concrete, or "realism." At one end of the continuum is a painting of a violin so perfectly rendered that we feel we could reach into the frame, pick up the instrument, and play it. At the other end is a canvas painted pure white or black all over. There is nothing in it to reach in and touch.