I'm really mixed on how to define it, to be honest. One the one hand, you could say it's an expression or exploration of human emotions, but then what does that make of painted portraits or landscape pictures, or pieces of photography that have a fantastic aesthetic effect but convey nothing beyond their own flamboyance? Would you deny those things the title of art? And to what point does the artists influence make it art? Does giving a woman's portrait an enigmatic smile make it art, when without it it would not be such?
But then, sheer craftmanship is not enough to make something qualify as art. Otherwise every tailored jacket or carpenter made chair could be placed in a gallery. Effort and technical proficiency isn't enough to raise it up, I mean, then you could easily make a case for Windows XP being a work of art. So perhaps, in agreement with Oscar Wilde's immortal words "All art is quite useless" as in it has no practical merit? But art can enlighten, inspire, challenge, teach, provoke, assure and much else besides. And what's more important? Being told how to exit the plane safely in the event of an emergency by a sequence of images, or being shown how to respect your fellow humans by 'To Kill a Mockingbird' or anything else that has a huge impact on you?
I suppose what I'm getting at here is that, for me, art is something that has no practical benefit to humanity (an intellectual benefit at most, I would never deny 1984's illuminating allegory the position of art) and requires a high degree of craftmanship to create. Exploration of ineffable truths and other high minded pursuits are optional as far as I'm concerned. I just put down my thoughts in a few minutes, so this is far from my comprehensive theory of art (if I even had one) and there are certainly many holes in my argument, but hopefully it can provoke discussion.