Language: English language collector's jargon
Damascus steel is a rather broad term that is used to describe steel, usually on blades or gun barrels, that exhibits a fancy pattern. The name probably refers to the city of Damascus through which wootz and pattern welded steel was at some point imported into Europe.
In gunsmithing a "damascus steel" barrel almost exclusively refers to a barrel made of twisted rods. See twist-core.
In antique knives and swords "damascus steel" usually refers to wootz steel which is a type of crucible steel that forms a watery pattern in the resulting steel. In this case, people often speak of "true damascus".
Alternatively "damascus steel" is often used for types of pattern welded steel that exhibit any kind of pattern. This is especially prevalent in modern bladesmithing circles.
Because the term is so broadly used for steels that were constructed in widely different methods, one might wonder whether the term is accurate enough for descriptions of antique arms. Especially because much better, more accurate descriptions for the various construction methods are available.
"Damascus steel" among antiques is perhaps best suited for marketing purposes and less so for a serious differentiation of steel constructions.