Shimaibakama (also called Shimaihakama) is a "hakama" (a kind of trousers worn with a kimono) of a special shape, mainly used in Noh drama. It got its name because it was often worn by performers playing Shimai dance, or Maibayashi dance.
Shimaibakama evolved from the general hakama for horse riding ("umanori bakama" in Japanese). For ease of movement the gusset is made lower, and a divider inside is made correspondingly higher. Stitching the first pleats ("ichi no hida" in Japanese) is a special method used when sewing the cloth to avoid wrinkles or twists when the wearer stands up.
When performing a Noh drama, the performers of the Hayashikata (people who play hayashi, or the musical accompaniment), Koken (a director of the drama performance) and Jiutai (Noh chorus) sections often wear a montsuki (a formal kimono with a family crest) and a shimaibakama. When worn in Kamishimo (a formal samurai attire consisting of a stiff, sleeveless jacket and a hakama), the hakama part is often made as a shimaibakama.
There is not much difference among styles regarding the method of making a shimaibakama, but one variation used in the UMEWAKA family line, Kanze school, is that the pleats are not sewn.
Sometimes a general hakama used for horse riding and a "mai bakama" used for Classical Japanese dance ("Nihonbuyo" in Japanese) are also called shimaibakama, but these are different from the shimaibakama used in Noh.