A milliner is someone who specializes in making what?

Hat-making or millinery is the design, manufacture, and sale of hats and other headwear. A person engaged in this trade is called a milliner or hatter. Historically, milliners produced or imported an inventory of garments for men, women, and children and sold these garments in a millinery shop. The millinery industry benefited from industrialization during the nineteenth century. Since the mass manufacturing of hats began, the term "milliner" is usually used to describe a person who applies traditional hand-craftsmanship to design, make, sell, or trim hats primarily for a mostly female clientele. Many prominent fashion designers, including Rose Bertin, Jeanne Lanvin, and Coco Chanel, began as milliners.

Source: Wikipedia