God spoke to Moses and said to him, “I am the Lord. I appeared to Abraham, Isaac and Jacob as El Shaddai, but I did not make Myself known to them by my Name [Yod, Hay, Vov, Hay].” (Exod. 6:2-3)
Judaism has always shown its reverence for the name of God by the tradition of not pronouncing it. Thus, the letters Yod, Hay, Vov, Hay are combined with the vowels for Elohim and the pronounced word Adoshem or “Lord” is substituted for the vocalization.