Japan Thread is a term for a type of metallic thread that is similar to the metals used in traditional metallic embroidery. Over the past several years Kreinik has greatly increased the number of colors of Japan Thread available (the picture is of the four newest) and the number of sizes.
Kreinik recently posted an article about Japan Threads and how to use them.
Japa Thread isn’t strong enough to go through needlepoint canvas much, but, as you can see by the picture in the article, it’s great for couching. There are lots of other great ideas in the post