Metalsmith is a category profession. It contains skills relating to the smelting of metals and alloys and the crafting of various metal products. Confusingly, the skill used for smithing furniture is also named "Metalsmith".
An adult dwarf whose best skill is in this category will be known as a "Metalsmith".
The metalsmith skill is used to make furniture, buckets, bins, blocks, cages, and anvils at a metalsmith's forge. (Despite their being under the "furniture" menu of a forge, chains are made by metal crafters, and animal traps are made by trappers).
Since the Metalsmithing labor covers not only this skill but also weaponsmith, armorsmith, and metal crafter, it may be difficult to control which dwarves perform each type of smithing task.