It is a cushion to sit on and to be used with tatami mats like a shiki-buton. It is a kind of futon especially designed for people to sit on, so the size is considerably smaller than a shiki-buton. If you sit directly on the tatami mats, you may tend to feel numbness in the legs, however, you can reduce the body pressure on the folded legs or buttocks while sitting in seiza style by laying just one piece of zabuton on the mats. Zabutons are called by different names with the size. There are names such as ko-zabuton, donsu-ban, and meoto-ban.