What is art? If you check the dictionary (which is an inane way to define something so subjective) you'd find a definition along the lines of "something beautiful or visually appealing" but that definition should frankly just be tossed out immediately. Ignoring the postmodern movement, there are pieces of art, that are universally regarded as art, that are not beautiful. This is maybe an unpopular opinion but let's take La Guernica by Picasso as an example.
This is "Invisible Sculpture" by Andy Warhol. The piece in question is not the white box, but what's resting on top of it: nothing. I remember getting into an discussion with a friend of mine after stumbling upon an article saying a similar piece, a blank white, floor to ceiling canvas, had been sold for quite a bit of money. The piece was also titled "invisible" and at the time I thought it was completely idiotic somebody would pay good money for a solid white stretched canvas. It was soon pointed out to me that I was maybe thinking about it too simplistically. When my friend saw the painting, or lack thereof, he was reminded of a child's imaginary friend. Invisible to the surrounding world, but the child could see them clearly. Maybe that's all art is. It derives meaning from those who can appreciate it and see its value. Whether or not everybody can see its value is irrelevant.
I in no way pretend to be an authority on what is or is not art but this definition works for me. I'll admit, it feels like a pretentious answer, but honestly isn't "what is art?" kind of a pretentious question?