A petticoat is a women's undergarment, generally designed to be slightly stiff, so that it will inflate skirts or dresses worn over it.  Petticoats and pantaloons have been in existence since at least the 1500 's. A woman wearing a petticoat has full, flounced skirts, along with the illusion of a slim waistline. Petticoats have been included in women's undergarments for centuries, waxing and waning in popularity. They are unlikely to disappear entirely, as full skirts and petticoats keep returning in the fashion cycle. Most large department stores carry petticoats, as do specialty stores, particularly stores which carry bridal fashions.

Women's fashion has included a petticoat or pantaloons since at least the 1500's . Women of all classes would have worn petticoats to inflate their skirts and enhance their privacy, especially in eras where women's underpants were still rare. The petticoat was typically made of a stiff material, so that it would prop up over skirts, or multiple layers of petticoats made from soft fabrics would be worn. The sheer volume of the multiple petticoats would certainly give overskirts more volume, but it was undoubtedly very hot, especially in the summer.

At a minimum, women usually wore at least three petticoats. In some eras, they were designed to be entirely invisible, hidden under the wearer's long skirts. In other instances, the bottom of the petticoat was meant to stick out, and it would be ornamented with lace, ribbons, or embroidery. In other eras, the front of the petticoat was designed to be visible through an open-fronted gown, slits in a dress or skirt, or looped skirts. These petticoats were, for a time, replaced with metal cage hoops  that were symmetrically shaped. later, in the mid 1800's the shape became fashionable to have a bustle effect in the back, and a flatter look in the front of the skirt. All the while, the "appearance" of a slim waist and a lengthening of the torso was achieved.