Realistic, abstract and nonobjective is another way to classify the subject matter of a painting. Abstract is a work that looks real, but has been distorted in some way. Works of art do not always easily fit into these categories. Think of these three terms on a line. Realism is on the left, abstract is in the middle and nonobjective is on the right.
Works of art can be on the term, beside the term or in between terms.
When we refer to these terms, just pick the one you think best fits. Look at the above examples again. Pigeons would be a realistic work. The artist tried to capture what he saw the best he could. The work by van Gogh is abstract.