A union suit is a type of one-piece underwear that covers your whole body, from your neck down to your wrists and ankles. Picture long underwear, but instead of separate tops and bottoms, it's all connected into a single garment that you step into and button up the front.

Union suits became popular in America in the late 1800s because they kept people warm in drafty houses and cold weather. Before central heating, staying warm meant wearing lots of layers, and a union suit provided full-body warmth without the bulk of separate undergarments.

The most famous feature of old-fashioned union suits was the “drop seat”: a flap in the back that could be unbuttoned for bathroom trips without having to remove the whole garment. While union suits were once everyday clothing for men, women, and children, today you mostly see them as cozy pajamas or worn by people working outdoors in very cold weather. In old cartoons and comics, characters often appear in red union suits with the drop seat flap, which became a humorous symbol of old-fashioned underwear.