"Fretted" means ornamented as with fretwork. Here is a portion of the Wikipedia explanation of "fretwork":Fretwork is an interlaced decorative design that is either carved in low relief on a solid background, or cut out with a fretsaw, jigsaw or scroll saw. Most fretwork patterns are geometric in design. . . . The term is also used for tracery on glazed windows and doors.
Black Fretwork Pattern Outdoor Rug by WANELO Night Sky