Hair

From Brickipedia, the LEGO Wiki.

The twin-bunned hair of Star Wars' Princess Leia, the colorful Anime hair of Exo-Force's Takeshi, and the classic short, long, and pony-tail hair.

Hair is a plastic lego piece that can be many shapes. It serves as a minifigure's hair. It is attached to the head to make the "top part".