Flattened depictions can be found in traditional black and white silhouettes, though white, any color, or a shade of gray might be used within the flat shapes. Form is only suggested by the outer boundaries of the flat shapes. Total flattening of objects often makes them into icons for the type of person, animal, object, etc. they are, de-emphasizing individuality.
Flat shapes for each object might be used to emphasize the abstract composition of the scene being depicted. The flatness might imply shallowness. Or it could highlight the isolation of one character from another.
Featured: The Artist’s Mother Opening a Door by Edouard Vuillard.