A costume designer is a person who designs costumes ... Well, certainly my definition is too basic. Here is portion of a definition that I found on Wikipedia. "A costume designer is a person whose responsibility is to design costumes for a film or stage production. He or she is considered part of the "production team", alongside the director, scenic and lighting designers as well as the sound designer. The costume designer might also collaborate with a hair/wig master or a makeup designer. In European theatre the role is somewhat different as the theatre designer will design both costume and scenic elements. Costume designers will typically seek to enhance a character's persona, and/or to create an evolving plot of colour, changing social status or period through the visual design of garments and other means of dressing, distoring and enhancing the body, The designer needs to possess strong artistic capabilities as well as a thorough knowledge of pattern development, draping, drafting, textiles and costume/fashion history." I modified this a bit. You can find the most current costume designer
definition at Wikipedia.
Children's Costumes Women's Costumes Men's Costumes