A corset cover was worn in the 19th and early 20th centuries to do just what it says - cover the corset and prevent the corset's hardware from damaging one's clothing. Corset covers are always white, and often trimmed with lace and/or embroidery, also white. Sometimes they may feature a pink or peach ribbon, and occasionally a blue one! They may sometimes have short or elbow length sleeves, or are sleeveless. They open down the front, usually closing with buttons or a combination of buttons and hooks.
Today, antique corset covers make beautiful, romantic and crisply cool summer blouses, and look fabulous with jeans.
See my blog post about antique underwear: