A miniskirt is a very short skirt, ending high on the thigh. The name became famous in the 1960s as young, bold fashion, and it is still the ordinary word for that length. People of different ages have never quite agreed about it: for some it is just clothes, for others it still feels daring. The word itself is everyday and informal. Fashion also talks about midi (to the mid-calf) and maxi (long), so mini here is about how much leg you see, not about a small person or a toy skirt. Though actually how short “mini” must be is a bit loose — one person’s miniskirt is another person’s merely short skirt — but everyone hears the word as “much shorter than a normal skirt.”