Abstract art, nonfigurative art, nonobjective art, and nonrepresentational art are loosely related terms. They are similar, but perhaps not of identical meaning. Abstract art uses a visual language of form, color and line to create a composition which may exist with a degree of independence from visual references in the world. Abstraction indicates a departure from reality in depiction of imagery in art. This departure from accurate representation can be slight, partial, or complete. Abstraction exists along a continuum. Even art that aims for verisimilitude of the highest degree can be said to be abstract, at least theoretically, since perfect representation is likely to be exceedingly elusive. Artwork which takes liberties, altering for instance color and form in ways that are conspicuous, can be said to be partially abstract. Total abstraction bears no trace of any reference to anything recognizable. (wikipedia)
In painting and sculpture, the term "representational art" usually refers to images that are clearly recognizable for what they purport to be, such as a human figure, a banana, a tree, and so on. Such images need not be true to life. So a tree does not have to be green, or even upright, but it must clearly represent or be recognizable as a tree. By contrast, non-representational or "abstract art" consists of images that have no clear identity, and must be interpreted by the viewer.