Asking "What is art?" is like asking "What is the meaning of life". It's a big, opinion driven, multifaceted question. Here is a thought worth chewing on:
Seeing as much of our understanding and communicating is visual... I think it is safe to see art as a universal language. One used for identity, common culture expression, aesthetics and invention. The one that intrigues me the most is invention. Art has been used as a vehicle for expressing invention forever. It is the fastest vehicle for conceptual thoughts to become representational or even tangible realities. Early Star trek invented the concept of the cell phone and Jule's vern novels and illustrations fueled a desire to create the submarine and space ship. But lets look past arts ability to create common understanding for future desires and look at invention in art. Jan Van Eyck's early point perspective, Leonardo's use of varnish layers, Monet's impressionism, Duchamp's urinal, Pablo's cubism...etc. Most commonly, fame in art comes down to who was first. First to try something. But if there is nothing new under the sun (a practical philosophy)... How can anything really be original? I think it comes down to invented process with existing materials. Take snow for example. When a kid sees snow it is an alien and beautiful disruption in their world. They see it new, but with each passing year the snow starts to loose its luster. A good artist realizes their art process must be inventive enough to disrupt the viewer and revitalize their interaction with subject. The artist must invent a new "lens" for the viewer to see the subject, emotion or idea. That's why good art is so visually exciting. You see the "snow" with the same enthusiasm as a 5 year old again. Subject matter might not matter, but its inventive process in art certainly does.