A specific type of traditional Japanese school uniform made up of a serafuku with a navy blue shirt, a (usually long) navy blue pleated skirt, and (most often, but by no means exclusively) a red neckerchief.
This classic design was very common in the mid-20th century, but was eventually replaced in most schools with the other, lighter styles that are more often seen today.
Should not be used for any old blue or partially blue serafuku. See blue_serafuku for that.