A petticoat is a garment similar to, and worn under, a skirt. In the fashions of western cultures before the 1920s, the petticoat was generally made of coarse plain fabric, and kept the outer dress (which was often made of more expensive and fragile material) from direct contact with the skin. If the woman needed to walk through damp or dirt, she could lift her outer dress, and it would be the cheap petticoat which would get dirty, while also preserving her modesty (i.e. preventing her legs from being seen). During some periods, a number of layers of petticoats were worn to produce a full-skirted fashion silhouette.
In a fetish context, a petticoat may be very frilly and designed to be partly visible under the skirt. It may make the skirt stand away from the body, and allow upskirt glimpses. It may even be worn without a skirt; petticoats designed for this purpose often resemble tutus. Petticoats are often part of French maid outfits.