In his book, “Playing to the Gallery,” the artist Grayson Perry attempts to answer this question. I'll summarize his definition because I found it interesting and challenging:
He begins by stating that it's now widely accepted that anything can be viewed as art. Seeing as that's an infinitely broad definition, he goes on to describe the following “scorecard” for what counts as art. A “yes” means it's more likely to be art:
* Is it in a gallery or an art context?
* Is it a boring version of something else? Does it lack entertainment value?
* Is it made by an artist?
* Is it limited edition?
* Is it admired by hipsters?
* If you put it in a dumpster, would a passer-by wonder why an artwork had been thrown away?
* Does it detain and suspend us in a state of frustration and ambivalence, making us pause and think rather than simply react?
* If it's a photograph that's smaller than 2m and costs less than five-figures, then it scores negatively.
He says that the above tests aren't watertight, but if you put them together in a Venn diagram, the bit in the middle (the bit to which all the answers are yes) is pretty well guaranteed to be contemporary art.
I dislike the definition, but I wonder if it might be accurate. When I try to come up with a better definition, I wonder if the concept I'm trying to describe is something else—what art _should be_—not what art is.