“[A] sleeveless garment worn like an apron worn over dress by women and children as protection against soiling.” (367)
According to the Berg Encyclopedia of World Dress and Fashion (2010), pinafores had significance outside of their function:

“Women’s and children’s clothes became status symbols showing the level of prosperity provided by the man’s income from his work and business. In buying goods for their children, families also declared that they invested in the future….. The pinafore, originally intended to protect against dirt, also became a fashionable garment, decorated with frills and lace and with a hem that curved up at the sides so the dress underneath would be seen.”