noun
bobbed hair; bob cut
A traditional Japanese hairstyle for girls, cut straight around the head at chin level. The name comes from its resemblance to the mythical kappa's hair style.
See also: 河童
彼女は髪をおかっぱにしている。
She wears her hair in a bob.
昔の少女はよくおかっぱ頭だった。
Girls in the old days often had bobbed hair.
ボブ is a modern Western-style bob cut, while おかっぱ specifically refers to the traditional Japanese straight-cut style.
From お (honorific prefix) + 河童 (kappa, a mythical water creature), because the hairstyle resembles the traditional depiction of a kappa's hair.