As the word implies, it means a picture frame made up of  two or more frames ( mouldings ) stacked, or put on top of each other, but, please read this post  "Someone mentioned picture frames with “stacked mouldings”, what are those? " . Referring to the image of the framed art in this post, you will note that there are two, disparate frames. The external, or outside one is of a light brown, or tan colour, the internal, or inner one, is of a warm cream colour.  The outside frame was built first, the inner one later. The picture framer then fitted the internal frame inside the external one.  Because mouldings  ...