A traditional women's fashion ensemble from turn-of-the-century Japan. It typically consists of a kimono (often with simple decorative patterns), a hakama skirt worn over it at the waist, and high laced boots, sometimes with a hair bow.
In the later years of the Meiji Era, the Japanese government began to encourage the establishment of women's junior high schools. Typical Japanese women's clothing at the time, however, was more showy and elaborate than modest or functional. As a result, this style quickly rose in popularity as a more practical alternative for women attending school. Even in the present day, it is traditional attire for women at some college graduation ceremonies, as seen here.
Despite the name of the tag, this is not explicitly worn by schoolgirls, and it is not restricted to depictions of the Meiji era (especially since the style remained popular into the Taisho era).
Although this outfit looks quite similar to some types of traditional Japanese waitress attire, the two should not be confused with one another (Although in some cases, it may be difficult). As a rule of thumb, if the girl in question is wearing tasuki or has rolled-up/pushed-up sleeves, then these may be indicators of a waitress uniform (as well as less-subtle signs such as name tags, menus, serving trays, etc.)