I find "what is art" discussions impossible to resolve and untangle from prejudices and biases. The least problematic answer I've found comes from John Carey, paraphrasing: "art is whatever someone has decided it to be". In other words, if I decide something is art, then it is.
The problem shifts slightly to a more interesting way to pose this question: why some art has more value than some other art (or even "does some art has more value than some other art")? Equally difficult to resolve but more prone to highlight prejudices and biases mentioned above.