The term "picture plane" refers to an imaginary, flat surface that serves as the background for a painting or other work of art. It is essentially the boundary between what is depicted in the image and what lies outside of it. The picture plane can be thought of as the edge of the canvas or paper on which the artwork is created, although it may also extend into three-dimensional space if the artist chooses to incorporate elements that protrude beyond the surface. In either case, the positioning and treatment of the picture plane play a significant role in determining the overall composition and visual impact of an artwork.