Abstract art is a very broad art movement. One of the first definitions was the complete stripdown of art from realism. The first artist to do this may have been Piet Mondrian with a use of pure straight lines, shapes and primary colors. You could say most art forms of whole 20th century are abstract, so its not that meaningful or well defined. In my own art, I have two abstract styles: Architectural Abstraction and Metal Mayhem. Architectural Abstraction is based off 30, 60 and 90 degree angles with a lot of action to it. Metal Mayhem is pure colors with very painful expression with metal tools.