trying to define "Abstract Art"

[simplex]

The term "abstract art" is like the term "modern music" in the sense that it is a very broad umbrella sheltering a wide variety of art. But like "abstract math," the general sense of the term is that it is the opposite of the concrete, or "realism."

(taken from .......http://www.artbylt.com/........
very nice and educative site by the way)