Couching is simply sewing a heavy thread in place with a finer thread. Its a retro technique, too, that was originally done by hand, but it works beautifully by machine as well. I use a zigzag stitch to secure the heavy thread in place.
Judy Martin: rough couching, over raveled weft threads, unseparated floss & narrow denim strips. Familiar threads & fabrics used in unfamiliar way. Usually used fr neat seam or mended pocket is used in a messy & raveled manner