what is dance?

I was thinking about Merce Cunningham today. I was mostly thinking about what exactly "dance" is. When I google searched it, I got a definition of "an artistic form of nonverbal communication". That is incredibly vague. Much like the term art, it can be extremely difficult to define. In a sense we could say that the simple act of walking. When I try to picture how Cunningham looks at dance, I imagine he might look at it as if it is a form of representing the world around him. Many of his dances that I have seen do this for example beach birds and ocean both portray the way mother nature acts.
The way I look at dancing as movement but always in effect with gravity. We make movements in respects to gravity, we jump and come back down due to gravity. We go on the point of our toe against gravity. We are constantly struggling with gravity and dance is a somewhat more graceful way of doing so.  Partly because I am in a astronomy class this semester, I have been interested in dancing in space with zero gravity, how would that effect the movements and performances. The lack of gravity would change the whole way we look at dancing and would create a whole new styles and forms of dancing.