(Hebrew יסוד means foundation) The ninth sephirah of the the Tree of Life (Kabbalah). In the macrocosmic universe, Yesod is the fourth dimension. In the microcosmic universe (man), Yesod corresponds to the sexual organs and to the Ethereal body. In the Bible, Yesod is Eden, the Promised Land.
"Yesod is the Vital or Ethereal Body. Yesod is the foundation of the Third Logos, the center where the sexual force of the Third Logos gravitates. The sexual forces which are the living foundation of our physiology gravitate in Yesod. The Holy Spirit abides in Yesod." - Samael Aun Weor
"And the king [Solomon] commanded, and they brought great stones, costly stones, [and] hewed stones, to lay the יסד [foundation] of the house." - 1 Kings 5:17
"By Chokmah [wisdom] in Yesod [foundation-sex] Iod-Havah hath founded the earth; by Binah [understanding] he established the heavens. By his [Daath-Gnosis] knowledge the depths are divided [into Abba and Aima, Father-Mother, Adam and Eve], and the clouds distillate the [semen] dew [in Yesod-sex]." - Proverbs 3