Works that are realistic have subject matter that the artist intends to represent the way things actually look. Some works from early in the history of art do not look 'real' but the artist's intent was to capture them realistically. In later works, such as this painting by Barend van der Meer, the effectiveness of artists to make works realistic are more evident.
Realistic does not mean that the subject matter is based on real things. A sculpture of the mythological goddess Aphrodite can still be realistically portrayed even though the subject is not real.