Wariza (割座), also known as "w-sitting" or "reverse tailor style sitting" in English, is a sitting posture whereby the butt is on the floor and the legs are bent backwards on each side of the body. It is the traditional informal sitting style for Japanese women. If the legs are folded out to only one side, then it is called yokozuwari.
The other Japanese names are: 女の子座り (onna-no-ko-zuwari, girl's sitting), アヒル座り (ahiru-zuwari, duck sitting) or ぺたん座り (petan-zuwari)
Read the full article.