My short definition is:
Joy is sturdy happiness.
I think it points off the map to the Divine.
Sometimes we have sparks of joy. Perhaps seeing the innocence in our children when we play with them in an unguarded moment, or in a perfect sunset, or some beautiful simple pleasure we love. It is not circumstantial, but exists under and even through the ups and downs of life's curvy road. And no, we don't always sense it, but when we rest in it, my goodness, what a blessing.