"full frock" costume for women refers to a dress, especially one that is a full-length or long-skirted dress, often considered a formal or elegant outfit. The term "frock" is an older and slightly more formal way of saying "dress" and is commonly used in British English. A "full frock" costume could be a formal evening gown, a ball gown, or any dress with a full skirt, especially those worn for special occasions.