A simple, common definition of "abstract art" is "not realistic." Yet many artists who call their work abstract, actually do have a subject in mind when they paint. They take a figure or landscape and simplify it, exaggerate it, or stylize it in some way. They are not trying to imitate nature, but to use nature as a starting off point. Color, line, and form are more important to them than the details of the actual subject matter. They want to give a sense or feel for the subject rather than an exact replication.