My current (evolving) definition:
Art is the ultimate physical expression of the human desire to enter and understand The Mystery, a desire that leaves an insatiable hunger, a yearning, to create within each of us. Entering the Mystery and expressing it is the only thing that will temporarily satisfy this hunger.
Art enables (and is the only channel that enables) humans to send our expressions of Resonance across space and time, to provide inspiration and energy (in the forms of beauty, symbols, and myth) to one another. Upon receiving these expressions of resonance, we interpret them as deep truth through our own unique experiences of reality, allowing us to also, even if only in our own minds, to express the Mystery in our own way.
The perception of the transcendent beauty of true art causes insight and positive mutations in our soul, the betterment of which is our true art. And we are able, in this way, to participate in the beautiful and terrifying ongoing symphony of transformation of the Cosmos.
How do you define art?
“Every genuine artistic intuition goes beyond what the senses perceive and, reaching beneath reality's surface, strives to interpret its hidden mystery. The intuition itself springs from the depths of the human soul, where the desire to give meaning to one's own life is joined by the fleeting vision of beauty and of the mysterious unity of things.” — Pope John Paul II