What is the term YHWH?
YHWH, are the four consonants which make up the divine name (Exodus 3:15; found more than 6,000 times in the Old Testament. The written Hebrew language did not include vowels, only consonants were used, therefore readers supplied the vowels as they read (this is true even of Hebrew newspapers today.) Reverence for the divine name led to the practice of avoiding its use. In time it was thought that the divine name was too holy to pronounce at all. Thus, the practice began using the word Adonai: "Lord." Many translations of the Bible followed this practice. In most English translations YHWH is recognizable where the word LORD appears in caps.
In the course of time over the centuries the actual pronunciation YHWH was lost. In the Middle Ages Jewish scholars developed a system of symbols placed under and beside the consonants to indicate the vowels. YHWH appeared with the vowels from "Adonai" as a device to remind them to say "Adonai" in their reading of the text. From the study of the structure of the Hebrew language most scholars today believe that YHWH was probably pronounced Yaheweh (Yah' weh).
Endnotes Holman Illustrated Bible Dictionary, 2003.