Yes "art" can be defined. It wouldn't even be a thing if it couldn't be defined. We wouldn't speak of it or have the concept. "Art" can refer to many different things though. Maybe you call something art just because it appeals to your subjective aesthetic sense, then it is "art" to you but it might not be art to another, but that doesn't mean it's undefined it's defined for a given individual at a given point in time. Still one could determine that art has to be communicating some sort of meaning or purpose as that is another reason people look at and label things "art".
Without a definition, art is literally "undefined". Hence we have no reason to talk about it. We can't say "This is art" or even the converse "This is not art". If we abandon the idea of defining what art is or can be, then we leave ourselves with no means of being able to identify true works of art. Many people would claim that attaching a definition to our concept of art limits our ability to understand or appreciate what art really is, but I believe this comes from a misunderstanding of the purpose of definition. When you search "define tree" on Google, the first definition listed is "a woody perennial plant, typically having a single stem or trunk growing to a considerable height and bearing lateral branches at some distance from the ground". This gives us an accurate way of identify trees when trying to distinguish trees from bushes or grass. But consider the overly miniature version of a tree, the bonsai tree. It fits all of the ideas of this definition except that of "growing to a considerable height". Does that mean that a bonsai tree is not a tree? Absolutely not. Everyone who has seen a tree when first encountering a bonsai tree says to themselves "I've never such a small tree before." No one breaks out there smart phone and looks up the definition of tree on Google and claims, "Oh well, it doesn't fit the definition perfectly, so it's not a tree." Everyone who has been around and understands the concept of a tree will attach the label to a bonsai tree. So, we can see that a specific tree is not limited by the definition we put to the general classification of "a tree". Therefore, the definition of an object or concept is not, in and of itself, essence of the object or concept being described. It is merely a tool for helping us identify if an object belongs to a group of other separate, yet similar objects. So I would suggest that we use this tool. We should define art so that someone who is "art illiterate" can have some idea of what art is, in order to begin understanding what human works of creation might foot-the-bill for being true works of art.
There are several ways you could define art, but my belief is that one definition will get you better definition that other and so on. Art plays a large part to make our lives infinitely rich and imagine just for a minute, a world without art! Art gives us way to be creative and express ourselves. Therefore art is something that makes us more thoughtful and well rounded humans. On the other hand, art is such a large part of our everyday lives that we may hardly even stop to think about it. Art is in a constant state of change, so nobody can pin down what it is. Art can’t be defined because different people think differently; art is a broad concept, and art changes over time.
No. Art comes from the mind of someone and cannot be defined. One person may see something totally different than another. The artist may have one idea on what the piece represents, whether it be music, a painting, or writing, and the viewer may see it in a whole light. Art is in the eye of the beholder.
No, I do not believe art is something that can easily be defined or made into a concrete thing. Art is abstract and it varies depending on the artist and medium. Art can literally be anything. Art depends on the artist and is, because of this, a very abstract and variable thing.
No, it can't be defined for the simple reason that everyone has different ideas about what defines art. Each person has different tastes and unique perceptions regarding art. Although I concede something that has no thought or effort put into it is hardly to be considered art. However, that is just my opinion and I'm sure there are others that would disagree.
Art can have some loose definitions that usually apply to it but it incorporates far too many things for anybody to ever be able to nail it down to a "if it doesn't do ___ it isn't art" definition. It's too subjective with too many different viewpoints regarding what qualifies.