It is difficult to define art because art has a lot of branches in it. Art is diverse ranging from music, acting and drawing. This makes it to have a variety of meanings. Read more about this on http://plato.stanford.edu/entries/art-definition/.
Art is personal, it does not matter about all the opinions around you. It's visceral, you either like it or you don't. Beauty, or ugliness or strangeness, oddities all of this touch's everyone differently. What is art for one person, is junk to another. Just to with your own opinion.
Actually, that's a really interesting question when you consider that art can be just like any other form of expression, such as writing. It's true that you can interpret a book in many different ways, but it's also true that it can't just be interpreted in just any way. The same is true of art. It has genres--"impressionistic, abstract, etc." so there is a guide as to the work's significance and its definition. To be honest, I think the reason people think art is so difficult to define is because they think that art is itself subjective (not in the 17th Century sense). But that's precisely the assumption that must be proved rather than disproved. Can you really say that "The Mona Lisa" or the paintings in the Sistine Chapel are difficult to define as art? Or is it rather that there are ways to determine what it is?
art is everything-if you look at it the right way. It is very hard to explain everything at the same time. without art earth is just EH. art is anything and everything. It doesn't have to be beautiful. It doesn't have to be something. You are surrounded by ART!
Art can come in many forms,Music,paintings,writing...I think it's so difficult because Art is defined by different people and different perspectives,there is no Unanimous definition,Each and everyone of us on this planet and(maybe)in another world have a different meaning for Art. That is why it's so hard to explain and define.
My daughter is an artist (animator-trained). Much of her earlier work is an expression of her feelings/interpretations of life at that time! Not an aggressor, when in high school, a girl picked on her. She went home and painted a girl (much like the girl @ school) spitting fire out of her mouth. If you look at a famous artist's work throughout their life, it shows different experiences. That is how art evolves and grows.
Art is all around you. Its God's creation. You are God's work of art. Art lives within the soul. It has no set definition. It has no boundaries or standards. Its what is beauty to you. You can take the ugliest picture and find beauty in its being. Art is an amazing thing. It can be simple, complex, it can be what ever you want it to be.