For me, personally ( and I think ART is really personal intrepretation) it is Story.

When I view works, whether online, in gallery or museum, I of course carry with my own cultural heritage and preconceptions of Life but these, in a way, our my tools to view art. And with these tools I make stories. I cannot help it. I love the intricacies in paintings filled with symbolism and many characters, but can also spend a good amount of time on say Monet's haystacks or waterlilies and cannot help but dream up underwater fairies or villages collected around the scenes.

Even were I to view dark abstract expressionism like Rothko , there'd be some drama that would eventually appear in my minds eye.

So, for me, art is Story and in most cases joyous, but also sometimes sad, much like life and honestly without the yin to the yang it'd be hard to appreciate many things.

Now, as to what is Art in the broad sense of the word, I'd say it can be a mirror of our times and political socio-economic climate, but not always. I guess I'd never really want to define Art on the broader spectrum as I'd not like to be presumptuous to assume what it Should be to a vast world.

Not a very concise answer, but that's my 2 cents. I do believe, with all my heart, that Art is important to us all, of that I can be sure.