Art is the abstraction of communication.
It is the broadest interpretation of understanding as a result of observation.
This upsets people because it means anything and everything is art in some sense, but that doesn't mean it's good art.
This upsets people further because they think art is subjective and that you can't reliably identify good vs bad art.
Good art is that which communicates effectively.
In the same sense art is the novel pursuit of objectivity or truth.
If you communicate effectively, there is objective understanding between people.
A painting of a sad scene, may make its author sad, but a good painting of a sad scene should communicate that abstract emotion to its audience.
In that way it has communicated some profound abstract truth beyond its physical composition.
This is a major hurdle for burgeoning artists to understand.
That it isn't necessarily the content of their product that represents their art, but how they express that content.
The construction of the plot of story is an art independent of the actual storytelling in putting it to page.
The powerful direction of a movie scene, doesn't come solely from the narrative context of the characters, but in staging and composition of the visual frame that they sit in.
A joke is not the punchline, but its delivery.
There's an Alan Moore quote or something, and it's probably bullshit but I think still truthfully and effectively illustrates an important aspect of "art".
Something like how in Sanskrit or some other primitive human language there is one singular word encompassing three distinctive concepts which in modern language have their own names: art, magic, and storytelling.
That art is magical or obscure in nature, one doesn't have to understand how it communicates for it communicate, distinguishing the consciousness from the unconscious, it may speak to a deeper part of you, and often times is more effective in doing so (see: Jung).
In the pursuit of objectivity we've created sciences and maths which are indeed mediums of art, but they have largely lost a lot of novelty.
They can encompass and reflect simple and powerful low-level objective truths, but there is more to truth than just physical attribution.
There are higher order or more abstract forms of truth, that are created from sentient perspective.
How to be a good person, how to frame cause and effect, how to rear a child, etc. which don't have simple answers but none the less have more correct solutions.
Art is the abstraction of communication.