Jehovah is a pronunciation of the Hebrew consonants of YHWH (the sacred Name of the God of Israel revealed in the Hebrew Bible) and the vowels of Adonai (Hebrew for “my Lord”).
When the Hebrew Bible was first written down in the Hebrew language, they wrote only with consonants, not vowels. So the sacred Name of God was written “YHWH” and likely was pronounced “Yahweh.” For millennia, Jews have gone to great lengths to avoid misusing the Name of their God, as he commanded them at the mountain after he delivered them from Egypt. At some point, ancient Jews began saying adonai (“my Lord”) when they saw “YHWH.” It wasn’t until the 10th century (as far as archaeologists have discovered) that a group of scholars called the Masoretes put vowels into the Hebrew text of the First Testament. They left the consonants “YHWH” in 7,000+ locations to show it was God’s Name. But they added the vowels of Adonai to the consonants to show later generations how to pronounce the word: “Adonai.” (That was why the Masoretes did their work of adding vowels; they were concerned that the number of scribes who could read Hebrew was unsustainably low, and they wanted to preserve what was read aloud by completing the text of what was written.) So Jehovah is a pronunciation of the vowels and consonants as they appear in the Masoretic Text, though it is not how the Jews would have known the Name of God.
Out of respect for the Jewish tradition of not uttering the sacred Name of God, the Committee on Bible Translation (CBT) for the NIV have chosen to display every instance of the Name YHWH in the Hebrew Bible as “Lord.”
“Lord” (kyrios) is how the Septuagint (or LXX; the third century BC Greek translation of the Hebrew Bible) translates YHWH. This led to the English solution of translating YHWH as “Lord,” which shows readers the difference between YHWH and adonai (written “Lord” or “lord” depending on context).
