Good call on the torii
It's a bit of a catchall meaning that metal is decorated by inserting contrasting metals -- most often silver and gold -- into its surface. I guess it also means the act of decorating metal with wavy patterns, which could be inlaid or etched.
I found this:
Pattern welding or Damascening, the traditional method for making decorative patterns on forged products, originated some hundred years before Christ. Early examples from the Orient show patterns resultant from the metallurgical processes used at ancient time. Later, melting and forging were developed so that skillful forge masters of around 500 AD could make the most artistic products by pattern welding.
Such damascene-forged swords or knives dominated the weapon industry from the Iron age to the Viking age. The possibilities of combining a hard edged material with a tough backing material were used. The magical image of the patterns made the owner feel invincible.
Steel pieces of at least two different compositions (Carbon or Phosphorous), were welded together and then kneaded by forging, producing a laminated material of about 100 layers. The patterns were made visible by etching the metal surface. Old swords and knives from the Viking or Anglo-Saxon periods often show magnificent patterns.
The name "Damascus" is attributed by some scholars to Damaskos, son of Hermes, who is said to have lived in this area and given it his name. Others attribute the name to the myth of Askos or that of Damas, who accompanied Dionysias, and offered him a skene (skin) thus the name "Damaskene". While others believe that the origin of the name came from Damakina, the wife of the god of water. Linguistically analysed, some feel that the name "Damascus" was derived from "The Water Land."
How the term came to also cover cuff links and brooches, IDK