It is a picture of a pipe, and while it conjures our memories and conceptualization of a pipe, it is, of course, merely a painting of one. Yet there is also the argument that when we see a physical pipe in person, it is only our “mind’s eye” view of a pipe that makes it a pipe. So, in some ways the difference between art and the “real world” is arbitrary. You can carry this as deep (as many layers of meta) or as shallow as you like, and that’s why the painting has inspired such a timeless continuing discussion over the decades of the meaning and significance of art.