This is a very good question If you think about it, all paintings are abstract art. The artist takes something that is 3-dimensional, a landscape, a still life, a person, and turns it into something that is 2-dimensional. Thus abstracting the essence of reality and creating a piece of art. There are of course, varying degrees of abstraction. A realist painter strives to make a painting that looks as exactly like the real thing as possible.While I admire their skill, and this is only my humble opinion, I don't really see the point of that, you may as well save a lot of time and effort and take a photograph. For me, abstracting the essence of a landscape is what it is all about. The other extreme of abstract art is where the finished painting bears no resemblance to anything, and is a (for some) a pleasing arrangement of shapes and colours. And if anyone asks, "but what is it", the answer is always "It's a painting".