Sentence:  We went into Mrs. Monmouth 's library , which had low bookshelves all along the walls , and above them a Modigliani portrait , a Jackson Pollock twelve feet long , and a gorgeous Miro with a yellow <WSD>background</WSD> , that looked like an inscription from a Martian tomb . 
Meaning of the word marked with <WSD> tags:  the part of a scene (or picture) that lies behind objects in the foreground