The name derives from their being worn by stereotypical characters in risqué burlesque dramas of the bedroom farce variety.

A wide variety of costumes are manufactured and marketed under the "French maid" description today. These range from comparatively modest dresses extending well down the thigh or above the knees to transparent chiffon nightgowns or outright lingerie ensembles that cover almost nothing.

The classic French Maid costume, however, is a very short and clingy dress (ideally silk satin, or closely resembling it) trimmed with shirred white lace. Typically, they including a tiny white apron attached to the dress; sometimes, the apron is even shaped like a heart, with white lace fringes on the hems and revealing neckline. The skirt area of the dress is usually pleated. If panties are worn with it, they are usually white and ruffled, and the dress is sometimes short enough to display them, especially when the woman bends over.

Common accessories include a frill worn in the hair, or a tiara, a feather duster, and sometimes white lace cuffs and collar. If the dress has sleeves, they are usually short and puffed shoulder puffs. A corset or a layered white petticoat may be worn under the dress. The ensemble is almost always completed with black fishnet stockings and black high heels.

The costumes are sometimes worn to costume parties and sometimes in BDSM sexual roleplay (whether on brief occasions or as a routine form of servitude to the woman's lover).

From Wikipedia