Seiza (正座, originallly written 正坐) means the act of sitting in the right posture as well as the sitting position itself, specifically the style of sitting with the knees together and the legs folded under the body.
正座（せいざ、元の用字は正坐）は、正しい姿勢で座ること、およびその座り方、特に膝を揃えて畳んだ座り方である。