Concept of classifying the subjects of tanka and contrasts with the field of shizenei which incorporates elements of nature such as mountains, rivers, plants and trees as well as flower, birds, the wind and the moon.
短歌の対象を分類する概念で、山川草木、花鳥風月等の自然を詠みこんだいわゆる自然詠と対照される分野であるとされる。