 This stance is quite often used for its fast turning speed.Sagi-ashi-dachi (鷺足立 Heron-foot stance) also known as Tsuru-ashi-dachi (鶴足立 Crane-foot stance)
This is the stance on one leg, where the other leg is raised and bent so that its foot touches the knee of the base leg.The exact form of contact between the foot and the knee depends on the style or even on the particular version of the kata where this stance is used.