I probably shouldn't wander into this without brushing up on Aristotle, Aquinas, and a few dozen others.  But hey, if I insisted on doing things like this right, I'd never get around to doing them at all.  So I'll pitch in off the cuff.

Art is that which captures the intangible meaning(s) behind thing(s).  Depiction becomes art only to the extent that it includes something of the intangible along with the depiction.  Art can of course exist entirely without depiction, or with non-representational depiction.

Either that, or art is merely a term one subjectively applies to expressions that one finds interesting.  Or, there's a much better definition out there that I haven't seen, or have seen and not understood.  
Definitely, one of the above explains what art is.  I think.

Tom K