Realism refers to the art movement that began in the Nineteenth Century which strives to represent the common and ordinary scenes of life without idealization or flattery.  It also refers to the effort to portray these scenes as accurately as possible reflecting what the eye actually sees. 

Realism was foreshadowed by both Caravaggio and Rembrandt but was sparked by the Burial at Ornans by Gustave Courbet in 1850.  It led to the Academic movement and one of its foremost American exponents was Thomas Eakins.  He went to extraordinary lengths to represent the ordinary and pioneered the depiction of natural male nude subjects in ordinary circumstances.