A mannequin is a model of a human being, or of a large part of a human body. The construction materials used to make mannequins vary widely, along with the size and realism of these models. They are probably most famous for their use in the fashion industry, but mannequins are also used in medical training, art, and dressmaking. They can be purchased from specialty shops or through auctions; another great source for mannequins is a struggling department store, which may be willing to give away its mannequins or sell them at a low cost if it goes out of business.

The spelling “manikin” is also correct, and it is derived from the same root word, the Dutch mannekijn, which means “little person.” Originally, the Dutch used the term to refer to dwarfs, but over time it was also used in reference to jointed artist's models of the human body which were used when real people were not available. By 1570, English speakers were using “manikin” to talk about artists' models, and in 1902, mannequin was picked up from the French to describe models used to display clothing at department stores.

A department store mannequin is typically made life-size, although its measurements may be rather small and sometimes even disproportionate. Clothes and accessories can be displayed on the mannequin to make these items more appealing; depending on the store, mannequins may or may not have heads. Some people find mannequin heads a bit unsettling or odd, leading stores to display clothing on headless bodies or torsos, while other stores require heads to display accessories like hats and headbands, or to make a display feel more realistic.

High-end department store mannequins are jointed so that they can be put into varying positions, and they come in a range of skin tones. Less costly versions are cast in plastic in a generic pose. An artist's mannequin, on the other hand, is usually fully jointed, so that the artist can pose it as needed. These manikins also come in a range of sizes, from hand-sized to life-sized. Numerous graduates of art school have used these mannequins as tools to learn about anatomy, perspective, and other aspects of their craft.

Mannequins are also sometimes called dummies or lay figures, depending on the region of the world that one is in. Medical professionals and engineers often refer to their models of people as dummies to differentiate them from mannequins, since they use specialized models with articulated joints and other features to make them behave more like real human bodies. In medical training, advanced mannequins are used to practice intubation skills, the placement of IV needles, and patient management; extremely sophisticated mannequins can even be programmed to demonstrate various symptoms and respond to treatment.