[kibwen]

While acknowledging that the question "what is art?" is an interminable quagmire, I'll say that art is any artifact that induces an emotion.

If an artist paints a wall white, and that doesn't induce any emotion, then it's not art.

If an artist paints a wall white and then tells you "hey, this is art", and that induces anger or frustration in you because you disagree, then it becomes art.

When the person above implies that this "makes you ask questions", the question in this case is "what is art?", which, as mentioned, is a contentious and interminable topic which itself arouses emotion, making it good fodder as a topic for art.