My definition is quite simple : creating emotion through form.
I insist on the word “form” and not “substance”. Here is a simple example : death. The simple fact of speaking about death in a movie, a book, or a game should evoke in any spectator a more or less strong emotion, depending on his personal experience, as every living being is sensitive to it. But different persons will react differently to it. With the addition of a specific form, the artist is able to create a deeper and more focused emotion, for instance by creating beforehand an empathy for the dying character, thereby making the sadness brought about by his death a more personal emotion than the one caused by the death of a character unknown to the spectator. The fact of organizing the work of art to create empathy before making the character die is indeed a formal technique for presenting a simple fact (the death of a human being), which would be a lot different if another technique was used instead. If the spectator sees the same character with antipathy, he would probably feel some kind of relief, or even satisfaction, when his death occurs.
There are as more variations in the way of presenting the death of a character than there are artists. The way of presenting death (the choice of words, the rhythm of the sentences, the framing, the lighting, the music, the silences or rather the dialogs of other protagonists, the description by an off-screen voice, or a simple contemplation) will have a strong impact on the way one might feel about the scene.
Obviously, any fact, idea or feeling is impacted by the way of presenting it (love, friendship, the birth of a child, fear, pollution, everyday life, tasting of coffee, etc…). A great artist is able to carry very strong emotions through very insignificant things (cf. Mona Lisa, a very ordinary-looking woman, but painted with so much finesse in her expression, with her eyes staring at the visitor).
One might argue that, since any representation necessarily has a form, any work is art. Following my definition, it’s partially true. But only partially, as most people would content themselves with presenting the thing using a form previously known, or ineptly trying to copy it. On the other hand, drawing one’s inspiration from other existing art pieces, mixing them, dissecting them, slicing them up, and finally merging them is a true process of artistic creation. Major masterpieces are those which seem to come out of the blue, with nobody able to determine their heritage. Those are the ones that stand throughout time and remain references in History.
Here is all the difficulty of artistic analysis of a piece of artwork : How to detect what is pure inspiration? How does this formal expression carry an emotion (and which emotion?) to the spectator? Or else, how does an artist draw his inspiration from his experience to get the best out of it? How does he gather these elements to serve his own purpose? Finally, we can also try to detect why a piece of work is only a plagiarism of another one, with no (or very few) personal influence form the artist. If you analyze any piece of work near you, it should be part of one of those three categories.
We will next talk of different form of artistic expression usually admitted, but in a different classification than the one commonly used (cf. Art classification (Wikipedia))