Eifu - Eifu

Japanese: 永不 - えいふ

…However, it was differentiated from Kawanari, which was tax-exempt land but became uncultivable due to flooding. Depending on the length of the period without cultivation, it was classified as Tofu, Nenpu, Jofu, and Eifu. Tofu meant fallow land for a short period of time, such as six months or a year, as in "summer crop failure." …

From 【Terrain Untended】

…This can be defined as land without owner in the narrow sense. In addition, fields that had been developed and left abandoned for long periods, known as "eternal waste" or "eternal waste," also became land without owner. However, there was a demand for development of land that was profitable and advantageous for the ownerless mountains, especially the Kuroyama mountains and wilderness, and the developers were granted private sovereignty. …

*Some of the terminology explanations that mention "eternity" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…ただ，非課税地であるが，洪水で耕作不能となった川成（かわなり）とは区別された。作付けしない期間の長短などにより，当不，年不（ねんぷ），常不，永不のような別がみられた。当不は，〈夏分不作〉のごとく，半年もしくは1年ぐらいの短期間の休耕地を意味した。…