The hairstyle where hair is twisted into a tight bun at the back of the head is called a chignon.
The word comes from the French chignon, meaning “bun.” In English, it often refers specifically to a low bun gathered at the nape of the neck, although modern chignons can sit higher on the back of the head. Hair is usually wrapped, pinned, and secured with hairpins, barrettes, or decorative accessories.
Chignons have a long history. A similar style was worn in ancient Greece, where Athenian women used gold or ivory hairpins to hold their hair in place. The style became fashionable in 19th-century England and was especially prominent during the 1860s. French dancer Cléo de Mérode helped popularize it in France during the 1890s.
A chignon is technically a type of bun, but the terms are not always interchangeable. “Bun” is the broad category, while “chignon” usually suggests a more arranged, elegant, or low-set version. French twists, topknots, and ordinary buns are related updos but have different shapes or placements.