The word “art” is a hard one to use properly, because it includes a multitude of media and wildly contrasting definitions. The technical definition is as follows: “the expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power.”
The problem with defining art is that art defies all limitations and assumptions. Art is a term that can refer to infinite possibilities. Saying something is art is a lot like saying something is a “thing.” It doesn’t mean a whole lot. There are so many media that can be considered art, you can’t really limit it to any finite number of canvases. Even an act could be considered art, if done with creativity and passion.
Even to say “art can have no constraints” is a constraint in itself. Of course art can be free and unrestrained, but the best art does follow rules. For instance, Shakespeare’s plays are most powerful if you understand the rules about meter and rhyme, and even the social rules of the time. And Mozart is average without understanding how pieces were usually written, and his own form that exist only within each piece. Creativity cannot prosper in the absence of limitations––it only works when limitations exist to be interpreted, bent, or broken. 
More tricky is distinguishing between levels of art. When people say high art, they refer to classical music, literature, and art, while low art refers to pop music, literature, and art. It’s the difference between Bach and the Backstreet Boys. High art is lofty and only enjoyed by few, low art is easily enjoyed by the masses. One issue with that is that it makes it sound like one is superior to the other; for instance, if someone claimed all orchestral music is more pure or moving than all pop music, they would be discrediting a huge amount of perfectly good music. 
A notable example of this is John Williams, the famous music composer, who created the soundtracks to countless famous movies, such as Star Wars, Jaws, Indiana Jones, Jurassic Park, and Harry Potter. Everyone knows and loves his soundtracks. Yet if you are familiar with orchestral repertoire, you realize many of his most famous motifs and melodies bear striking similarities to famous orchestral pieces, including Debussy’s La Meer, Holst’s The Planets, and Dvořák’s Symphony no. 9, “From The New World.” A group of contemporary orchestral music critics criticized him for making low art of high art. In a move to be taken seriously by high art contemporaries, Mr. Williams composed a series of pieces, all of which were entirely abstract, atonal, and, frankly, not very good. In my opinion, Prince should be placed on the same level as Mozart, and Breaking Bad on the same level as Dickens. 
I have neither time nor space to go into great depth about this topic, but before I conclude I want to mention the issue of distinguishing good art from bad art. I don’t think that it’s good to label art as good or bad based on your personal opinions regarding it, as many critics do, but even worse is to say all art is created equal, because it certainly is not––if someone personally enjoys reading the Percy Jackson series, and they hate reading Great Expectations, to claim The Lightning Thief is a better novel would be folly, whether or not this someone is a freshman in high school. To properly judge art, you have to analyze the goal of the piece in question, and the effect of the piece. If that sounds like too much work, you can always just say “I hated this book” rather than “This book is awful,” the latter of which I hear far too much. Frankly put, Percy Jackson and Great Expectations are two completely different works with completely different intentions. One can only look at each in reference to itself and other works with similar intentions.
Art is complicated. Many people would have wrapped this up by leaving everything up to the readers,  and saying its all up to how you see it, but I have more faith in myself to give a satisfying conclusion. Art is up to personal preference––I cannot claim to be better than someone else just because I’d rather listen to Jazz than Country––but there is good and bad art, beyond the limits of high and low art. Batman v. Superman exists, and it’s an example of terrible pop art. Someone might enjoy it, but it’s still bad art, kindly put. It is not necessary to engage art intellectually to enjoy it. Everyone has the freedom to like what they will like, regardless of its universal quality. However, to judge, to speak with authority about something, requires a lot of consideration and contemplation.