A hairstyle, hairdo, or haircut refers to the styling

Fashion

Fashion, a general term for a currently popular style or practice, especially in clothing, foot wear, or accessories. Fashion references to anything that is the current trend in look and dress up of a person...

 of hair

Hair

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

, usually on the human head. The fashioning of hair can be considered an aspect of personal grooming

Personal grooming

Personal grooming is the art of cleaning, grooming, and maintaining parts of the body. It is a species-typical behavior that is controlled by neural circuits in the brain.- In humans :...

, fashion

Fashion

Fashion, a general term for a currently popular style or practice, especially in clothing, foot wear, or accessories. Fashion references to anything that is the current trend in look and dress up of a person...

, and cosmetics

Cosmetics

Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...

, although practical, cultural, and popular considerations also influence some hairstyles.
Throughout history, people have worn their hair in a wide variety of ways, largely determined by the fashions of the culture they live in.