The term for a hairstyle in which hair is woven into a single plait is a braid. Braiding involves dividing hair into sections and crossing those sections over one another in a repeated pattern, creating a structure that holds the hair together.
A basic three-strand braid is made by alternately moving the outside strands across the center. More elaborate forms include the French braid, which incorporates additional hair as the braid progresses, and the Dutch braid, in which sections are crossed under the center so the braid appears raised. Fishtail and four-strand braids use different weaving patterns but are still types of braiding.
A braid is not the same as a twist: a twist generally wraps sections around one another without the repeated over-and-under plaiting used in a braid. A bun is hair gathered and coiled into a rounded shape, while a ponytail is hair secured together without necessarily being woven.
Braiding is both a practical and decorative technique. It can keep hair controlled, protect it from tangling, and form the basis of styles used in many cultures around the world.