A hairpin is a type of fastener that consists of two pieces of metal, usually made from wire or plastic, bent into an inverted U-shape. It can be used to hold hair in place by inserting it through the hair and securing it with bobby pins or clips. The term "hairpin" is also sometimes used figuratively to describe a sudden change or twist in a situation or storyline, similar to how one might use a hairpin turn on a road to make a quick change of direction.