It is named against Tomitsu (eastern esotericism), which is Shingon Esoteric Buddhism that has To-ji Temple in Kyoto as konpon dojo-seminary (basic hall of training), and was started by Saicho, who was the founder of the Nihon Tendai Sect (Japanese Tendai Sect).
京都東寺を根本道場とした真言密教を東密と呼ぶのに対する呼称であり、日本天台宗の開祖である最澄によって創始されたものである。